[Refactor] nvm_alias, nvm_resolve_alias: use builtins

[Tests] `nvm_alias`, `nvm_resolve_alias`: add edge-case tests

nvm_alias() used a sed/awk pipeline to strip comments and blank lines from alias files that almost always contain a single word.
A while-read loop with parameter expansion does the same filtering more directly.

nvm_resolve_alias() piped nvm_alias through head and tail to extract one line, and used printf/grep for cycle detection.
Parameter expansion and a case statement replace both without the extra plumbing.

All replacements are POSIX (read -r, case, IFS=, parameter expansion).
As a side effect, this also removes 4 external process invocations during shell init.

[Fix] `nvm_resolve_alias`: detect cycles via newline-anchored `case`

The original commit referenced above changed SEEN_ALIASES from `\n`-delimited
storage (interpreted by `printf '%b' | nvm_grep -e "^${name}$"`) to space-
delimited but left the line-anchored grep in place — without newlines in
the haystack the anchored pattern can never match, so cycles never break.

Switch to literal-newline storage and a `case` pattern anchored on those
newlines. Newline anchoring also handles alias names containing spaces,
which token-based patterns false-positive on (e.g. lookup of `bar` matches
substring " bar " inside " foo bar midway " when the chain visits the
multi-token alias `foo bar`).

New test file covers self-loop, multi-hop loop, cycle through a
space-bearing alias name, and a non-cycle through a space-bearing
alias name. Existing `test/fast/Aliases/circular/` fixtures continue
to pass.

test/fast/Aliases/nvm_alias handles comment-only alias file

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create an alias file containing only comments
+printf '# this is a comment\n# another comment\n' > ../../../alias/test-edge-comments
+ACTUAL="$(nvm_alias test-edge-comments 2>/dev/null)"
+EXIT_CODE="$(nvm_alias test-edge-comments 2>/dev/null; echo $?)"
+[ -z "${ACTUAL}" ] || die "expected empty output for comment-only alias file, got >${ACTUAL}<"
+[ "${EXIT_CODE}" = '0' ] || die "expected exit code 0, got ${EXIT_CODE}"
+
+rm -f ../../../alias/test-edge-comments

test/fast/Aliases/nvm_alias handles empty alias file

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create an empty alias file
+printf '' > ../../../alias/test-edge-empty
+ACTUAL="$(nvm_alias test-edge-empty 2>/dev/null)"
+EXIT_CODE="$(nvm_alias test-edge-empty 2>/dev/null; echo $?)"
+[ -z "${ACTUAL}" ] || die "expected empty output for empty alias file, got >${ACTUAL}<"
+[ "${EXIT_CODE}" = '0' ] || die "expected exit code 0, got ${EXIT_CODE}"
+
+rm -f ../../../alias/test-edge-empty

test/fast/Aliases/nvm_alias strips trailing whitespace

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create an alias file with trailing spaces and tabs
+printf '22.1.0   \t \n' > ../../../alias/test-edge-trailing-ws
+ACTUAL="$(nvm_alias test-edge-trailing-ws)"
+EXPECTED='22.1.0'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}<, got >${ACTUAL}<"
+
+rm -f ../../../alias/test-edge-trailing-ws

test/fast/Aliases/nvm_resolve_alias handles cycles

@@ -0,0 +1,52 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# 1-hop self-reference: alias points to itself
+echo 'self' > '../../../alias/self'
+
+ACTUAL="$(nvm_resolve_alias self)"
+EXPECTED='∞'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for self-reference, got >${ACTUAL}<"
+
+rm -f '../../../alias/self'
+
+# Multi-hop loop: link1 -> link2 -> link3 -> link1
+echo 'link2' > '../../../alias/link1'
+echo 'link3' > '../../../alias/link2'
+echo 'link1' > '../../../alias/link3'
+
+ACTUAL="$(nvm_resolve_alias link1)"
+EXPECTED='∞'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for 3-hop cycle, got >${ACTUAL}<"
+
+rm -f '../../../alias/link1' '../../../alias/link2' '../../../alias/link3'
+
+# Cycle through an alias name containing a space
+echo 'midway' > '../../../alias/foo bar'
+echo 'foo bar' > '../../../alias/midway'
+
+ACTUAL="$(nvm_resolve_alias 'foo bar')"
+EXPECTED='∞'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for space-name cycle, got >${ACTUAL}<"
+
+rm -f '../../../alias/foo bar' '../../../alias/midway'
+
+# Non-cycle through an alias name containing a space.
+# Token-based cycle detection would false-positive on this chain because
+# 'bar' appears as a substring of the multi-token alias name 'foo bar'.
+# Resolves: 'foo bar' -> 'midway' -> 'bar' -> 0.0.99
+echo 'midway' > '../../../alias/foo bar'
+echo 'bar' > '../../../alias/midway'
+echo '0.0.99' > '../../../alias/bar'
+
+ACTUAL="$(nvm_resolve_alias 'foo bar')"
+EXPECTED='v0.0.99'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for space-name chain, got >${ACTUAL}<"
+
+rm -f '../../../alias/foo bar' '../../../alias/midway' '../../../alias/bar'

test/fast/Aliases/nvm_resolve_alias handles deep chain

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create a 4-deep alias chain: hop1 -> hop2 -> hop3 -> hop4 -> 0.0.99
+echo 'hop2' > ../../../alias/hop1
+echo 'hop3' > ../../../alias/hop2
+echo 'hop4' > ../../../alias/hop3
+echo '0.0.99' > ../../../alias/hop4
+
+ACTUAL="$(nvm_resolve_alias hop1)"
+EXPECTED='v0.0.99'
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}< for 4-deep chain, got >${ACTUAL}<"
+
+rm -f ../../../alias/hop1 ../../../alias/hop2 ../../../alias/hop3 ../../../alias/hop4

test/fast/Aliases/nvm_resolve_alias with nonexistent target

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+die () { echo "$@" ; exit 1; }
+
+export NVM_DIR="$(cd ../../.. && pwd)"
+
+: nvm.sh
+\. "${NVM_DIR}/nvm.sh"
+
+# Create an alias pointing to a version that does not exist as an alias
+echo '99.99.99' > ../../../alias/test-edge-noexist
+
+ACTUAL="$(nvm_resolve_alias test-edge-noexist)"
+EXPECTED='v99.99.99'
+EXIT_CODE="$(nvm_resolve_alias test-edge-noexist >/dev/null 2>&1; echo $?)"
+[ "${ACTUAL}" = "${EXPECTED}" ] || die "expected >${EXPECTED}<, got >${ACTUAL}<"
+[ "${EXIT_CODE}" = '0' ] || die "expected exit code 0, got ${EXIT_CODE}"
+
+rm -f ../../../alias/test-edge-noexist