Fix all clippy warnings and format code with cargo fmt

[Copilot]

This PR resolves all clippy warnings when running cargo clippy --workspace --all-targets -- -D warnings and formats the codebase using cargo fmt.

Issues Fixed

Non-local Implementation Definitions

Moved impl Environment for TestEnvironment blocks outside of functions in test files to comply with Rust's scoping rules:

• crates/pet-poetry/tests/common.rs
• crates/pet-pyenv/tests/common.rs
• crates/pet-conda/tests/common.rs

Pointer Argument Optimizations

Replaced &String parameters with &str for better performance and idiomatic Rust:

• crates/pet/tests/common.rs: Functions does_version_match, get_version, is_valid_version
• crates/pet-conda/tests/ci_test.rs: Function get_version

Field Assignment Improvements

Replaced field assignments on Default::default() with struct initialization syntax:

• crates/pet/tests/ci_test.rs: Configuration objects (2 instances)
• crates/pet/tests/ci_poetry.rs: Configuration objects (2 instances)

Code Deduplication

Combined identical conditional blocks that had the same behavior for known issues:

• crates/pet/tests/ci_test.rs: Merged duplicate error handling for GitHub issue Issues with detection of Python on codespaces #64

Unnecessary Code Removal

• Removed needless ..Default::default() syntax where all struct fields were explicitly specified in crates/pet-pyenv/tests/pyenv_test.rs
• Removed unnecessary return statement in crates/pet/tests/ci_test.rs
• Fixed empty line after outer attribute in crates/pet-poetry/tests/config_test.rs

Configuration Fix

Added missing ci feature to crates/pet-poetry/Cargo.toml to resolve unexpected cfg condition warnings for CI-related conditional compilation.

Verification

All changes maintain existing functionality while improving code quality and performance. The build now passes cleanly with:

cargo clippy --workspace --all-targets -- -D warnings

Code has been formatted consistently across the workspace using cargo fmt --all.

Created from VS Code via the GitHub Pull Request extension.

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