Add Valkey as a storage backend for CrewAI memory

Summary

Add Valkey as a storage backend for CrewAI's memory system — a vector-search-capable store for short/long-term memory, plus a shared cache usable by A2A and file uploads. Valkey is an open-source, BSD-licensed fork of Redis, so this gives users a self-hostable, license-clean alternative to the existing storage options.

Opening this to track the work per @Vidit-Ostwal's request while the repo cleanup and the third-party-integration/configuration discussion are underway.

Status: implementation essentially complete

The work is already built, tested, and split across four open PRs (broken up at an earlier reviewer's request for smaller, easier-to-review diffs). They are rebased on latest main, CI is green, and CodeRabbit has passed. Best reviewed in order:

• #5700 — shared cache config + ValkeyCache (foundation for A2A and file uploads)
• #5701 — harden memory tool input validation
• #5702 — async-safe embeddings + resilient drain_writes
• #5703 — ValkeyStorage vector memory backend (depends on #5700 and #5702)

Notes

• No changes are needed from maintainers right now — this issue is for tracking. I understand the third-party-provider/configuration direction is still under internal discussion, and I'm happy to adapt the PRs (e.g. how the backend is registered/configured) to fit whatever pattern you land on.
• The implementation uses Valkey-GLIDE and the Valkey Search module for vector similarity (FLAT/HNSW), with scope/category/metadata filtering.