feat(luas): standalone mode, embedding, and luarocks support

[pgagnidze]

Summary

• Add standalone mode with --main flag (no rockspec needed)
• Add data file embedding with --embed flag
• Support absolute paths for luarocks modules
• Add cache hashing for reproducible builds
• Add parallel package fetching

New capabilities

Standalone mode:

luas -m app.lua lib/ -c lfs -t linux-x86_64 myapp

Embed data files:

luas -m app.lua -e templates/ -e config.json myapp

local embed = require("luas.embed")
local html = embed.read("templates/page.html")

LuaRocks modules:

luas -m app.lua ~/.luarocks/share/lua/5.4/inspect.lua myapp
luas -m app.lua ~/.luarocks/share/lua/5.4/pl/ myapp

Test plan

• Standalone mode builds and runs correctly
• Embedded files accessible at runtime
• LuaRocks paths compute correct module names
• Existing rockspec mode still works
• Cross-compilation works with all new features