build(benchmarks): add setup_luaport.sh to build luaport against lua@5.4

[davydog187]

Why

mix deps.compile luaport fails on a stock brew install lua setup, even with PKG_CONFIG_PATH set. Two reasons:

1. Wrong Lua version. brew install lua ships Lua 5.5; luaport 1.6.3 supports only LuaJIT or Lua 5.4. Its Makefile pkg-configs luajit by default.
2. API drift. Even against Lua 5.4, deps/luaport/c_src/luaport.c:517 uses LUA_GLOBALSINDEX, which Lua removed in 5.2.

PKG_CONFIG_PATH alone can't fix either — DEFINES := … in the luaport Makefile uses := so the LuaJIT-only LUAP_BIT/LUAP_FFI flags can't be overridden from the env, and the LUA_GLOBALSINDEX issue is in C source.

What

• benchmarks/setup_luaport.sh — idempotent shell script that:
  • locates Homebrew's lua@5.4 prefix,
  • patches deps/luaport/Makefile to pkg-config lua-5.4 (Homebrew's package name) and drop the LuaJIT-only LUAP_BIT/LUAP_FFI defines,
  • patches deps/luaport/c_src/luaport.c to replace the single LUA_GLOBALSINDEX use with lua_pushglobaltable + lua_rawset(L, -3),
  • runs MIX_ENV=benchmark mix deps.compile luaport --force.
• benchmarks/{closures,fibonacci,oop,string_ops,table_ops}.exs — updated the # NOTE: header in all five files to point at the new one-liner workflow.

Workflow now

brew install lua@5.4
./benchmarks/setup_luaport.sh
MIX_ENV=benchmark mix run benchmarks/fibonacci.exs

Verification

Ran the full clean cycle (mix deps.clean luaport → mix deps.get → ./benchmarks/setup_luaport.sh) and then each of the five benchmarks. All five now show a C Lua (luaport) column. Re-running the script on an already-patched tree is a no-op (guarded by grep on the use site, not the explanatory comment).

Fibonacci result for reference:

C Lua (luaport)   38.51 ips    25.97 ms
luerl              1.40 ips   716.84 ms    27.61x slower
lua (eval)         1.16 ips   859.34 ms    33.09x slower
lua (chunk)        1.15 ips   869.29 ms    33.48x slower

Caveat

The patches live under deps/luaport/, which mix deps.clean luaport will wipe. The script is idempotent, so the workflow after any deps churn is just ./benchmarks/setup_luaport.sh. A more durable fix would be a forked luaport on a branch, but that adds a fork to maintain. Happy to do that if preferred.