refactor(core): improve TwoFactorMiddleware clarity and maintainability

[joshtrichards]

• Resolves: #

Summary

Rewrites the beforeController for improved clarity and maintainability while preserving all intended/existing behaviors:

• removes the extra nesting and indirection
• eliminates redundant code paths
• breaks out all bypasses returns clearly
• restructures conditional checks for readability
• adds helpful, consistent inline comments throughout
• adds useful, but still brief class and method level doc blocks

No logic is missing or altered in a way that would break original policy:

• Bypass and enforcement flows are consistent.
• All existing controller/method name checks, user session logic, provider enforcement, etc., are fully represented
• All edge case behavior is preserved

TODO

• Integrate feat(core): add support for NoTwoFactorRequired attribute in TwoFactorMiddleware #57301
• Drop poll bypass for 2FA Notification app after fix: Add NoTwoFactorRequired attribute to poll method twofactor_nextcloud_notification#1151

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)