fix: remove nightly-only feature attributes

[nberlette]

• fix: remove nightly-only feature attributes
• fix(cow_str): remove unstable const impls from CowStr
• docs(cow_str): add safety documentation to unsafe CowStr methods
• tests(cow_str): remove duplicate InlineStr tests from CowStr
• fix(inline_str): respect feature-gated derive_more impls
• fix(inline_str): remove unstable const impls
• docs(inline_str): add safety and panic info to InlineStr docs
• tests(inline_str): improve InlineStr tests for 32-bit targets
• deps: add serde_json to dev dependencies for tests
• chore: bump version
• ci: add check/release workflow

[Copilot]

Pull request overview

This PR stabilizes the codebase by removing nightly-only Rust features and improving documentation for unsafe operations. Key changes include removing unstable const trait implementations, adding comprehensive safety documentation to unsafe methods, and improving test coverage for 32-bit architectures.

• Removes nightly-only feature gates (const_convert, const_index, const_trait_impl) to stabilize the crate
• Adds safety documentation to all unsafe methods in CowStr and InlineStr
• Improves test coverage with platform-specific tests for 32-bit targets

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/lib.rs	Removes nightly-only feature attributes to enable stable Rust compilation
src/inline_str.rs	Removes unstable const implementations, adds safety docs, makes derive_more features optional, and adds 32-bit tests
src/cow_str.rs	Removes unstable const implementations, adds safety documentation to unsafe methods, and removes duplicate tests
Cargo.toml	Bumps version to 0.2.0 and adds serde_json dev dependency
.github/workflows/ci.yml	Adds comprehensive CI/CD workflow for checking, testing, and releasing

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