Document Cloudflare KV query caching

[prdai]

What changed

• document the first-party Cloudflare Workers KV query cache adapter
• add Wrangler KV binding configuration and adapter setup examples
• explain explicit and global cache strategies and per-query expiration overrides
• document supported expiration options and unsupported Redis-specific options
• call out Workers KV eventual consistency and invalidation behavior
• update every dialect-specific cache guide consistently

Why

The ORM change for drizzle-team/drizzle-orm#5758 adds a Cloudflare-native cache option for Workers applications. The public documentation needs to explain how to bind KV, configure the adapter, and choose workloads that tolerate KV's consistency model.

Validation

• prettier --check on all six modified MDX files
• astro check (zero errors)