feat: Support business window constraint

[kibertoad]

fixes #770

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin and the Code of conduct

[Copilot]

Pull request overview

Adds support for restricting auto-merge behavior to a configurable “business hours” window, addressing #770 by introducing a 5-field cron-based merge window with optional IANA timezone evaluation. When outside the configured window, the action skips merging and exposes a distinct merge_status.

Changes:

• Introduces merge-window / merge-window-timezone inputs and documents them.
• Adds a cron parser + time-window evaluator (src/mergeWindow.js) with unit tests.
• Integrates merge-window evaluation into the action flow and adds a new skip status (skipped:outside_merge_window).

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/util.test.js	Adds coverage for new input parsing/whitespace trimming.
test/mergeWindow.test.js	Adds unit tests for cron parsing and window matching behavior.
test/action.test.js	Adds action-level behavior tests for skipping/merging based on merge-window.
src/util.js	Adds new inputs to getInputs() and new merge status constant.
src/mergeWindow.js	Implements cron parsing and “is now within merge window” logic.
src/action.js	Skips merge when outside the configured merge window; sets output status + log.
README.md	Documents new inputs, output status, and provides usage guidance.
dist/index.js	Bundled output updated to include merge-window feature.
action.yml	Declares new action inputs for merge-window and timezone.

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[simoneb]

LGTM