Mutate NonZero<T> generic return types

[sourcefrog]

Summary

• Support the generic NonZero<T> form (stabilized in Rust 1.79) in addition to the existing NonZeroUsize, NonZeroI32, etc. type-specific matching
• When T is a known unsigned type, generate 1; when signed, generate 1 and -1; when T is unknown, assume it could be signed and generate both
• Adds tests for unsigned, signed, and unknown type parameter cases

Closes #595

Test plan

• Unit tests for NonZero<u32>, NonZero<usize>, std::num::NonZero<u8> (unsigned)
• Unit tests for NonZero<i32>, NonZero<isize>, std::num::NonZero<i64> (signed)
• Unit test for NonZero<T> with unknown type parameter
• All existing tests continue to pass

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds mutation-generation support for Rust’s generic std::num::NonZero<T> return types (in addition to the existing NonZeroU32, NonZeroIsize, etc. matching), plus accompanying unit tests. Also updates release metadata to 27.0.0.

Changes:

• Extend type_replacements to recognize NonZero<T> and generate appropriate non-zero integer candidates based on whether T is signed/unsigned/unknown.
• Add unit tests covering unsigned, signed, and unknown generic NonZero<T> cases.
• Bump crate version and update changelog/release metadata for 27.0.0.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/fnvalue.rs	Adds NonZero<T> detection and new tests validating generated replacement expressions.
NEWS.md	Updates top-of-file release section to 27.0.0 with a release date.
Cargo.toml	Bumps package version from 27.0.0-pre to 27.0.0.
Cargo.lock	Updates the lockfile entry to reflect the new package version.

Comments suppressed due to low confidence (1)

NEWS.md:9

• The 27.0.0 changelog entry doesn’t mention the new NonZero<T> mutation support added in this PR. Consider adding a bullet (e.g., New/Fixed) describing the generic NonZero<T> return-type replacements so the release notes reflect the user-visible change.

## 27.0.0

Released 2026-03-07.

- Changed: Command line values for `--file`, `--exclude`, `--examine-re`, and `--exclude-re` are now combined with, rather than replacing, values given in the configuration file, consistently with every other option that takes a list. (Use `--config=OTHER` or `--no-config` to avoid using values in the configuration.) Thanks to @sandersaares for pointing this out.

- New: `--Zmutate-file` lists the mutants generated from a single Rust source file in text or JSON, without reading or requiring a containing package. This is intended as an aid for developing and debugging mutation patterns.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The NonZero<T> branch repeats the same two-value vec![1.try_into()..., (-1).try_into()...] construction in multiple places. Consider extracting this into a small local variable/helper to reduce duplication and make future tweaks (e.g., additional candidate values) less error-prone.