test: expand compatibility coverage and enforce Meteor type contracts

[dr-dimitru]

Summary

• Add standalone KeyDB/Valkey CI and optional configured Mongo-compatible endpoint tests.
• Handle Mongo URI query options in test database selection.
• Run Meteor TypeScript runtime tests and actual tsc adapter/shutdown contract checks separately.
• Clarify exact coverage and unverified cloud-service compatibility.
• Includes reviewed feature dependencies; merge after both feature PRs.

Verification

• Combined full npm test with Redis, MongoDB, PostgreSQL passed.
• Adapter guards and prepublish build passed.
• Type mutation check rejects a RedisAdapter missing acquireLock.
• Focused ESLint correctness rules passed; legacy .eslintrc is not supported by installed ESLint 10.

[dr-dimitru]

Additional local verification on the combined tree: 202/202 Jest tests passed with a dedicated three-master Redis Cluster plus standalone Redis, MongoDB, and PostgreSQL; 94/94 Meteor 3.4 default-suite tests passed. Packed tarball contains only expected runtime sources, declarations, README, LICENSE, and package.json. Measured line coverage is 97.62%, below the aspirational 99% target. No package published.