feat: add is_github_actions env helper

[ReenigneArcher]

Description

Introduce a new public is_github_actions() API that detects GitHub Actions by checking for the GITHUB_ACTIONS environment variable. The implementation is added in env.cpp, documented in the public header, covered with tests for both present and missing variable cases, and shown in the README usage example.

Screenshot

Issues Fixed or Closed

Roadmap Issues

Type of Change

• feat: New feature (non-breaking change which adds functionality)
• fix: Bug fix (non-breaking change which fixes an issue)
• docs: Documentation only changes
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semicolons, etc.)
• refactor: Code change that neither fixes a bug nor adds a feature
• perf: Code change that improves performance
• test: Adding missing tests or correcting existing tests
• build: Changes that affect the build system or external dependencies
• ci: Changes to CI configuration files and scripts
• chore: Other changes that don't modify src or test files
• revert: Reverts a previous commit
• BREAKING CHANGE: Introduces a breaking change (can be combined with any type above)

Checklist

• Code follows the style guidelines of this project
• Code has been self-reviewed
• Code has been commented, particularly in hard-to-understand areas
• Code docstring/documentation-blocks for new or existing methods/components have been added or updated
• Unit tests have been added or updated for any new or modified functionality

AI Usage

See our AI usage policy.

• None: No AI tools were used in creating this PR
• Light: AI provided minor assistance (formatting, simple suggestions)
• Moderate: AI helped with code generation or debugging specific parts
• Heavy: AI generated most or all of the code changes

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (070f94c) to head (1f49d2c).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #40   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          213       217    +4     
  Branches        12        13    +1     
=========================================
+ Hits           213       217    +4     

Flag	Coverage Δ
Linux-Clang	85.71% <66.66%> (-1.79%)	⬇️
Linux-GCC	100.00% <100.00%> (ø)
Linux-python	100.00% <ø> (ø)
Windows-MSVC	100.00% <100.00%> (ø)
Windows-MinGW-UCRT64	100.00% <100.00%> (ø)
Windows-python	100.00% <ø> (ø)
macOS	85.71% <66.66%> (-1.79%)	⬇️
macOS-python	100.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/common/env.cpp	100.00% <100.00%> (ø)

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