Update MSRV to Rust 1.82 and replace once_cell with std equivalents

[Copilot]

This PR updates the Minimum Supported Rust Version (MSRV) to 1.82 and replaces most usages of the once_cell crate with standard library equivalents that are now available in stable Rust.

Changes

MSRV Update

Updated rust-version from various versions (1.70, 1.74) to 1.82 in 78 Cargo.toml files across the repository.

once_cell Replacements

Replaced all 26 instances of once_cell::sync::Lazy with std::sync::LazyLock (stable since Rust 1.80):

• gix-tempfile/src/{lib.rs, signal.rs}
• tests/tools/src/lib.rs
• gix-path/src/env/{mod.rs, git/mod.rs, auxiliary.rs}
• gix/src/interrupt.rs
• src/shared.rs
• tests/it/src/commands/check_mode.rs
• Various test files throughout the repository

Why OnceCell Remains

The OnceCell type in gix-features/src/threading.rs continues to use once_cell because std::sync::OnceLock::get_or_try_init() is not yet stable in Rust (tracking issue: rust-lang/rust#109737). This method is essential for error handling during lazy initialization in multiple places throughout the codebase, particularly in gix/src/config/cache/access.rs.

Once get_or_try_init() is stabilized, we can complete the migration by updating the OnceCell type aliases to use std::sync::OnceLock and std::cell::OnceCell.

Dependency Cleanup

Removed the once_cell dependency from 12 Cargo.toml files where it's no longer needed. The dependency is retained only in gix-features (with the once_cell feature flag) to support the OnceCell type until the standard library API is fully stabilized.

Testing

• ✅ Entire workspace builds successfully
• ✅ All tests pass for modified packages
• ✅ No regressions introduced

Original prompt

@GitoxideLabs/gitoxide/issues/2216 Update the MSRV to Rust 1.82, and then replace usages of once_cell with std::cell::OnceCell or std::sync::LazyLock where possible.

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