#41717 fix(federation): endpoints rejecting valid requests

Proposed changes (including videos or screenshots)

Issue(s)

CORE-2549

Steps to test or reproduce

Further comments

Summary by CodeRabbit

• Bug Fixes
  • Improved Matrix federation request validation for room history backfill and message pagination.
  • Fixed valid image thumbnail requests that were previously rejected.
  • Improved acceptance of cross-homeserver room invitations.
  • Enhanced send-join request validation to support valid federation events.