Support package library path dependencies

[godofecht]

Summary

• add pkg_library_paths to model package-provided prebuilt library search paths
• apply optional os and arch guards before adding lazy package paths to compile artifacts
• extend zig-gamedev executable parity to cover zgpu, artifact:zgpu:zdawn, and the real dawn_aarch64_macos prebuilt path
• update schema, project docs, huge corpus docs, and generated site docs

Validation

• zig build test --summary all
• /Users/abhishekshivakumar/zig/0.14.1/zig build test --summary all
• /Users/abhishekshivakumar/vex_zig/.toolchains/zig-aarch64-macos-0.15.2/zig build test --summary all
• /Users/abhishekshivakumar/vex_zig/.toolchains/zig-aarch64-macos-0.16.0/zig build test --summary all
• tools/huge_corpus.py --prepare --repo zig-gamedev --root /tmp/azazel-huge-forks-10
• tools/huge_corpus.py --executable-parity --repo zig-gamedev --root /tmp/azazel-huge-forks-10
• tools/huge_corpus.py --executable-parity --root /tmp/azazel-huge-forks-10
• tools/huge_corpus.py --plan --roadmap --root /tmp/azazel-huge-forks-10 --expect-count 10
• python3 scripts/build_site.py
• PYTHONPYCACHEPREFIX=/tmp/azazel-pycache python3 -m py_compile tools/huge_corpus.py scripts/build_site.py
• git diff --check