Wire up rustler_precompiled for v0.3.0

[qweliant]

What changed

lib/lib_raw/nif.ex

Switched from use Rustler to use RustlerPrecompiled. On install, Hex will
now download a precompiled .so from the GitHub release instead of invoking
the Rust toolchain. Key options:

Option	Value
crate	libraw_nif
version	read from Mix.Project.config()[:version] (currently "0.3.0")
base_url	https://github.com/qweliant/libraw/releases/download/v<version>
nif_versions	["2.15", "2.16", "2.17"] (OTP 23 / 24-25 / 26+)
targets	see table below
force_build	true when LIBRAW_BUILD=1 (source-build opt-in)

:rustler is kept as a dep — rustler_precompiled needs it for source-build fallback.

.github/workflows/release.yml

Triggers on any v* tag push. Build matrix: 4 targets × 3 NIF versions = 12 jobs, all on native runners.

Target	Runner	libraw install
aarch64-apple-darwin	macos-latest (Apple Silicon)	brew install libraw
x86_64-apple-darwin	macos-13 (Intel)	brew install libraw
x86_64-unknown-linux-gnu	ubuntu-22.04	apt-get install libraw-dev
aarch64-unknown-linux-gnu	ubuntu-24.04-arm (native ARM64)	apt-get install libraw-dev

Uses philss/rustler-precompiled-action@v1 to compile and package each NIF artifact, then a separate release job collects all artifacts and publishes the GitHub Release via softprops/action-gh-release@v1.

README.md

• Prerequisites: clarified that libraw is always required but Rust is not (for supported targets).
• Installation: version constraint updated to ~> 0.3, new "Supported Platforms" table, LIBRAW_BUILD=1 source-build instructions.

mix.exs

@version bumped "0.2.0" → "0.3.0".

CHANGELOG.md

Added v0.3.0 entry.

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libraw-still-required caveat

libraw is dynamically linked at runtime (LGPL). Every machine that runs
:libraw must have the shared library installed:

# macOS
brew install libraw

# Debian / Ubuntu
apt install libraw-dev

The precompiled NIF does not bundle or statically link libraw. This is by design.

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MUSL / Alpine

Intentionally excluded — libraw is not reliable on musl libc.

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Pre-merge checklist

• Cut a v0.3.0-rc1 tag and verify all 12 workflow jobs pass
• Confirm .tar.gz + .sha256sum artifacts appear on the draft GitHub Release
• Test mix deps.get && mix deps.compile on a clean macOS machine without Rust — should download precompiled NIF, no Rust invocation
• Test same on a clean Linux x86_64 machine without Rust
• Test LIBRAW_BUILD=1 mix deps.compile forces a source build (requires Rust + libraw-dev)
• Verify LibRaw.decode/2 and LibRaw.metadata/1 work end-to-end after precompiled install
• Confirm mix hex.publish package includes checksum.exs (generated by mix rustler_precompiled.download LibRaw.NIF --all --print)
• Remove draft status and merge
• Publish to Hex (mix hex.publish)

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Generated by Claude Code