Docs: add and align missing @ since annotations across Two-Factor providers

[masteradhoc]

What?

This PR adds and aligns missing @since annotations in provider docblocks across the Two-Factor plugin.
It also includes minor docblock formatting cleanup to keep inline documentation consistent and readable in code review.

Why?

Several provider methods were missing @since tags or had inconsistent version annotations.
This made historical tracking harder for maintainers and contributors, especially when reviewing API evolution and backport relevance.

How?

• Added missing @since tags to provider class/method docblocks.
• Updated selected @since values to the correct historical versions.
• Cleaned docblock indentation/formatting where needed for consistent PHPCS-friendly style.
• Kept changes documentation-only (no functional behavior changes).

Testing Instructions

1. Review changed provider files and confirm each touched docblock has a valid @since line.
2. Confirm version values match intended release history.

Screenshots or screencast

N/A (documentation-only change).

Changelog Entry

Changed - Added and normalized missing @since annotations in provider docblocks for clearer API/version history documentation.

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Co-authored-by: masteradhoc <masteradhoc@git.wordpress.org>
Co-authored-by: georgestephanis <georgestephanis@git.wordpress.org>

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[georgestephanis]

Lot of work to add these, much appreciated though!

(or is there some automated tool that digs back through versions? either way, cool!)

[masteradhoc]

@georgestephanis manually, but was faster then expected!