feat: add Copilot instructions and guidelines for unit tests and release notes

.github/prompts/create-release-notes.prompt.md

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+# Create Release Notes
+
+You are an expert technical writer tasked with creating release notes for
+updates to this repository. Your specific task is to generate release notes that
+are clear, concise, and useful for developers and users of the project.
+
+## Guidelines
+
+Ensure you adhere to the following guidelines when creating release notes:
+
+- Use a clear and consistent format for the release notes
+- Include a summary of the changes made in the release
+- Highlight any new features, improvements, or bug fixes
+- If applicable, include instructions for upgrading or migrating to the new
+  version
+- Use technical language that is appropriate for the audience, but avoid jargon
+  that may not be understood by all users
+- Ensure that the release notes are easy to read and navigate
+- Include relevant issue or PR numbers where applicable
+- Use proper Markdown formatting
+- Use code blocks for commands, configuration examples, or code changes
+- Use note and warning callouts for important information
+
+## Versioning
+
+GitHub Actions are versioned using branch and tag names. The version in the
+project's `package.json` should reflect the changes made in the codebase and
+follow [Semantic Versioning](https://semver.org/) principles. Depending on the
+nature of the changes, please make sure to adjust the release notes accordingly:
+
+- For **major** changes, include a detailed description of the breaking changes
+  and how users can adapt to them
+- For **minor** changes, highlight new features and improvements
+- For **patch** changes, focus on bug fixes and minor improvements

.github/prompts/unit-test.prompt.md

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+# Create Unit Test(s)
+
+You are an expert software engineer tasked with creating unit tests for the
+repository. Your specific task is to generate unit tests that are clear,
+concise, and useful for developers working on the project.
+
+## Guidelines
+
+Ensure you adhere to the following guidelines when creating unit tests:
+
+- Use a clear and consistent format for the unit tests
+- Include a summary of the functionality being tested
+- Use descriptive test names that clearly convey their purpose
+- Ensure tests cover both the main path of success and edge cases
+- Use proper assertions to validate the expected outcomes
+- Use `jest` for writing and running tests
+- Place unit tests in the `__tests__` directory
+- Use fixtures for any necessary test data, placed in the `__fixtures__`
+  directory
+
+## Example
+
+Use the following as an example of how to structure your unit tests:
+
+```typescript
+/**
+ * Unit tests for the action's main functionality, src/main.ts
+ */
+import { jest } from '@jest/globals'
+import * as core from '../__fixtures__/core.js'
+import { wait } from '../__fixtures__/wait.js'
+
+// Mocks should be declared before the module being tested is imported.
+jest.unstable_mockModule('@actions/core', () => core)
+jest.unstable_mockModule('../src/wait.js', () => ({ wait }))
+
+// The module being tested should be imported dynamically. This ensures that the
+// mocks are used in place of any actual dependencies.
+const { run } = await import('../src/main.js')
+
+describe('main.ts', () => {
+  beforeEach(() => {
+    // Set the action's inputs as return values from core.getInput().
+    core.getInput.mockImplementation(() => '500')
+
+    // Mock the wait function so that it does not actually wait.
+    wait.mockImplementation(() => Promise.resolve('done!'))
+  })
+
+  afterEach(() => {
+    jest.resetAllMocks()
+  })
+
+  it('Sets the time output', async () => {
+    await run()
+
+    // Verify the time output was set.
+    expect(core.setOutput).toHaveBeenNthCalledWith(
+      1,
+      'time',
+      // Simple regex to match a time string in the format HH:MM:SS.
+      expect.stringMatching(/^\d{2}:\d{2}:\d{2}/)
+    )
+  })
+
+  it('Sets a failed status', async () => {
+    // Clear the getInput mock and return an invalid value.
+    core.getInput.mockClear().mockReturnValueOnce('this is not a number')
+
+    // Clear the wait mock and return a rejected promise.
+    wait
+      .mockClear()
+      .mockRejectedValueOnce(new Error('milliseconds is not a number'))
+
+    await run()
+
+    // Verify that the action was marked as failed.
+    expect(core.setFailed).toHaveBeenNthCalledWith(
+      1,
+      'milliseconds is not a number'
+    )
+  })
+})
+```