This pull request makes the "Requires at least" and "Requires PHP" fields in the WordPress plugin readme header optional, updates validation and documentation accordingly, and bumps the extension version to 0.1.9. It also adds tests to confirm the new optional behavior.

Validation and Parsing Changes:

• Made the requiresAtLeast and requiresPHP fields in the ReadmeHeader interface optional, allowing them to be omitted or empty, and adjusted the parser so missing "Requires at least" no longer triggers an error. [1] [2]
• Updated the validator to remove "requiresAtLeast" from the list of required fields.

Documentation Updates:

• Updated the README.md to clarify that "Requires at least" and "Requires PHP" are now optional, and that format validation still applies if present.
• Added a changelog entry for version 0.1.9 describing these changes and updated the comparison links. [1] [2]

Testing:

• Added a test to confirm that omitting "Requires at least" does not produce a validation error. [1] [2]

Release:

• Bumped the extension version to 0.1.9 in package.json.