SQLite: harden durability, add multi-file tenancy, and enforce file-based configuration

[mysticmind]

SQLite Changes Included

• Durable scheduling fixes:
  • improved scheduled timestamp precision and SQLite time comparisons to avoid early dequeue edge cases
  • updated scheduled/expiry movement logic to be consistent and deterministic
• GUID/id matching hardening:
  • normalized SQLite TEXT GUID comparisons in message-store batch operations (delete/reassign/dead-letter paths) to avoid case mismatch issues
• Saga durability fixes:
  • made SQLite saga schema initialization transaction-safe
  • ensured saga schema/data-source setup works consistently without ad hoc warm-up logic
• Breaking API simplification (intentional):
  • removed SQLite schema knobs that were misleading/not meaningful in practice
  • UseSqlitePersistenceAndTransport is now effectively connection-string focused
• New SQLite multi-tenant support with separate files:
  • added tenant-aware message store resolution for per-tenant SQLite files
  • added tenant-aware queue sender/listener implementations for SQLite transport
  • queue setup/listening/sending now works across active tenant databases
• Enforced file-based SQLite policy:
  • added centralized guard to reject in-memory SQLite connection strings (Mode=Memory, :memory: variants)
  • applied validation to primary config and tenant config paths (static, master-table seed, dynamic tenant source)
• Test-suite consolidation and modernization:
  • moved SQLite tests to reusable file-based DB helpers
  • added simple black-box E2E workflows for message, transport, saga, and multi-tenant multi-file behavior
  • renamed workflow test files/classes to neutral names (no file_based* prefix)
• Docs + mdsnippets updates:
  • updated SQLite durability guide to reflect connection-string-only/file-based direction
  • added/updated snippet-backed examples for transport, tenancy, tenant sends, and polling
  • removed in-memory recommendation from SQLite docs