build: add ci workflow for cygwin build and test

[tomghuang]

This patch introduces a workflow that verifies argtable3 can be built and tested using Cygwin on Windows. Both Debug and Release configurations are built and tested. The workflow ensures Cygwin compatibility and test coverage on every change.

[Copilot]

Pull Request Overview

Adds a new GitHub Actions workflow to ensure argtable3 builds and runs tests under Cygwin on Windows in both Debug and Release modes.

• Introduces .github/workflows/cygwin.yml to install Cygwin dependencies, configure via CMake, build, and execute tests.
• Uses a matrix strategy for Release and Debug builds.
• Validates Cygwin compatibility on every push, pull request, or manual dispatch.

Comments suppressed due to low confidence (1)

.github/workflows/cygwin.yml:6

• Verify that master is the correct default branch name—many repos now use main. If the default is main, update this to avoid missing workflow runs.

branches: [ master ]

[Copilot]

Environment variables set via $GITHUB_ENV are typically uppercased on Windows runners. Consider using CYGWIN_PATH (uppercase) and reference it as ${{ env.CYGWIN_PATH }} to ensure the variable is recognized consistently.

Suggested change

	echo "cygwin_path=$(cygpath -u "$GITHUB_WORKSPACE")" >> $GITHUB_ENV
	echo "CYGWIN_PATH=$(cygpath -u "$GITHUB_WORKSPACE")" >> $GITHUB_ENV

[Copilot]

[nitpick] The full shell path is repeated across multiple steps. Extract this into a workflow-level variable or default shell setting to simplify updates and reduce duplication.

Suggested change

	shell: C:\cygwin64\bin\bash.exe --login -eo pipefail {0}
	run: |
	echo "cygwin_path=$(cygpath -u "$GITHUB_WORKSPACE")" >> $GITHUB_ENV
	- name: Configure with CMake (Cygwin)
	shell: C:\cygwin64\bin\bash.exe --login -eo pipefail {0}
	run: |
	echo "cygwin_path=$(cygpath -u "$GITHUB_WORKSPACE")" >> $GITHUB_ENV
	- name: Configure with CMake (Cygwin)

[Copilot]

[nitpick] Consider adding caching for Cygwin packages between runs to speed up subsequent CI executions, for example by leveraging action cache for the /usr or package directory.

Suggested change

	steps:
	steps:
	- name: Cache Cygwin packages
	uses: actions/cache@v3
	with:
	path: |
	C:/cygwin64/var/cache/setup
	C:/cygwin64/usr
	key: cygwin-${{ runner.os }}-${{ hashFiles('**/.github/workflows/cygwin.yml') }}
	restore-keys: |
	cygwin-${{ runner.os }}-

[tomghuang]

It may take too long if we add this Cygwin workflow in CI. Close this pull request.