feat: allow explicit use of package managers

[2bndy5]

The adds 2 new CLI options (for both cpp-linter and clang-tools binaries):

1. --mod-sys defaults to the value of a CI env var (if present); allows enabling package managers in non-CI contexts.
2. --no-mod-sys strictly disallow use of package-managers; overrides the default value of --mod-sys.

Using both options in 1 invocation causes a conflict error.

resolves #364

Summary by CodeRabbit

• New Features
  • Added --mod-sys and --no-mod-sys CLI flags to control whether system package managers are used for clang tool installation. System package manager usage is automatically enabled in CI environments unless explicitly disabled via --no-mod-sys.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds an allow_system_package_manager: bool parameter to RequestedVersion::eval_tool that gates the try_install_package code path. The clang-tools-manager binary exposes this via a new --mod-sys CLI flag (with implicit CI detection), and the cpp-linter crate adds corresponding --mod-sys and --no-mod-sys flags with independent CI env-variable logic. The clap dependency gains the env feature to support environment-variable binding.

Changes

System Package Manager Opt-In Flag

Layer / File(s)	Summary
eval_tool signature and conditional gate clang-tools-manager/src/version.rs, clang-tools-manager/Cargo.toml	RequestedVersion::eval_tool gains allow_system_package_manager: bool; try_install_package is now called only when that flag is true. clap's env feature is enabled to support environment-variable binding.
clang-tools-manager CLI and wiring clang-tools-manager/src/main.rs	CliOptions gains mod_sys: bool with --mod-sys flag that conflicts with --no-mod-sys. The install loop computes the boolean from options.mod_sys, options.no_mod_sys, and the CI env var, then passes it to eval_tool.
clang-tools-manager test updates clang-tools-manager/src/version.rs	Test imports include std::env. All eval_tool invocations in tests pass the new boolean: false for eval_no_value and eval_download_path; runtime CI-derived value for eval_version.
cpp-linter CLI and run logic cpp-linter/src/cli/mod.rs, cpp-linter/src/run.rs	GeneralOptions gains mod_sys and no_mod_sys fields with mutually exclusive --mod-sys and --no-mod-sys flags. Verbosity doc is clarified. run_main computes the boolean from these flags and the CI env var, then passes it to capture_clang_tools_output.
cpp-linter clang_tools integration cpp-linter/src/clang_tools/mod.rs	capture_clang_tools_output gains modify_system: bool parameter. Both clang-tidy and clang-format version discovery paths pass this flag to eval_tool. Test helper test_db_parse passes false.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• cpp-linter/cpp-linter-rs#52: Both PRs modify the same cpp-linter/src/clang_tools/mod.rs::capture_clang_tools_output signature and its call sites, with overlapping code-level changes to function parameters and threading logic.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Linked Issues check	✅ Passed	The PR fully implements the requirements from issue #364: it introduces --mod-sys and --no-mod-sys flags, ensures system package managers are only attempted by default in CI environments, and allows explicit opt-in/opt-out control.
Out of Scope Changes check	✅ Passed	All code changes are directly related to the objectives of adding system package manager control flags and threading the allow_system_package_manager parameter through the relevant functions.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Title check	✅ Passed	The title clearly summarizes the main change: adding explicit control over package manager usage through new CLI flags.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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[codecov]

Codecov Report

❌ Patch coverage is 92.59259% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.43%. Comparing base (959ae38) to head (8d961f2).

Files with missing lines	Patch %	Lines
clang-tools-manager/src/version.rs	94.73%	1 Missing ⚠️
cpp-linter/src/run.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #372   +/-   ##
=======================================
  Coverage   92.42%   92.43%           
=======================================
  Files          23       23           
  Lines        3632     3649   +17     
=======================================
+ Hits         3357     3373   +16     
- Misses        275      276    +1     

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