Add core/users ability

[jorgefilipecosta]

What?

• Adds a read-only core/users ability with single-user lookup by id, user_email, user_login, or user_nicename.
• Adds collection mode with optional roles, has_published_posts, page, per_page, and fields; omitted REST input defaults to empty collection mode.
• Uses WP_User-shaped field names, including user_login, user_email, user_nicename, user_url, and user_registered, to align with Core’s existing core/get-user-info ability.
• Gates sensitive identifiers and fields against Core REST users behavior, omits inaccessible fields per user, excludes capabilities/meta, and respects get_option( 'show_avatars' ).
• Adds PHPUnit and browser-level Abilities API coverage.

Testing

• php -l includes/Abilities/Users/Users.php
• php -l includes/Main.php
• php -l tests/Integration/Includes/Abilities/Users/UsersTest.php
• vendor/bin/phpcs --standard=phpcs.xml.dist includes/Abilities/Users/Users.php includes/Main.php tests/Integration/Includes/Abilities/Users/UsersTest.php
• vendor/bin/phpstan analyse --memory-limit=1G includes/Abilities/Users/Users.php tests/Integration/Includes/Abilities/Users/UsersTest.php
• npx wp-scripts lint-js tests/e2e/specs/abilities/core-users.spec.js
• npm run test:php -- --filter UsersTest
• npm run test:e2e -- tests/e2e/specs/abilities/core-users.spec.js --project=chromium
• git diff --check

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

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[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 94.78458% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.68%. Comparing base (dd7d364) to head (078efd2).

Files with missing lines	Patch %	Lines
includes/Abilities/Users/Users.php	94.77%	23 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #774      +/-   ##
=============================================
+ Coverage      76.71%   77.68%   +0.97%     
- Complexity      1828     1941     +113     
=============================================
  Files             87       88       +1     
  Lines           7764     8205     +441     
=============================================
+ Hits            5956     6374     +418     
- Misses          1808     1831      +23     

Flag	Coverage Δ
unit	77.68% <94.78%> (+0.97%)	⬆️

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