v0.2.0: API overhaul, proper error handling, and CI

[meszmate]

Summary

• Breaking API changes: compress and decompress now return Result<usize, Error> instead of raw usize, with a dedicated Error enum (LibLoadError, FunctionLoadError, CompressFailed, DecompressFailed) that implements Display and std::error::Error
• FFI signatures corrected to match oodle2.h 2.9.11 — parameters use isize instead of usize, and unused callback/userdata args are properly typed as *const c_void / *mut c_void
• New API surface: decompress_with_options for explicit fuzz-safe/CRC/verbosity/thread-phase control, get_decode_buffer_size, and get_compress_scratch_mem_bound
• Library no longer leaked: Oodle now owns the Library directly (no more Box::leak), and stores raw fn pointers instead of Symbol references; Oodle is verified Send + Sync at compile time
• Oodle::load accepts impl AsRef instead of &str, matching libloading::Library::new
• All enums gain #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)] and use #[repr(i32)]; OodleCompressor adds Invalid and None variants; OodleCompressionLevel adds HyperFast4–HyperFast1
• Dependency update: libloading 0.7 -> 0.8 (drops winapi in favor of windows-link)
• CI: Added GitHub Actions workflows for fmt/clippy/build+test (Ubuntu, Windows, macOS) and crates.io publish on tag push
• Tests: Unit tests for enum discriminants, trait impls, and error types; integration tests (gated behind #[ignore] + OODLE_LIB_PATH env var) for compress/decompress roundtrips, decode buffer size, scratch mem bound, and invalid-data error handling
• README rewritten with installation, usage examples, compressor/level tables, error handling docs, and test instructions
• Cleanup: .gitignore simplified, Cargo.toml adds categories