Fix UnifiedJedis watch transaction state

[hutiefang76]

Fixes #3392

UnifiedJedis.watch() pins a connection by creating a transaction object before MULTI. The connection therefore reported queueing too early, so reads between WATCH and MULTI polluted the expected EXEC result count.

This change distinguishes WATCH-only state from an active MULTI transaction. Commands before MULTI run immediately on the pinned connection, while incompatible pipeline, subscription, and cursor operations are rejected.

Tests cover typed and raw reads, EXEC result alignment, pipeline/subscription guards, and SCAN variants. The focused Jedis suite passes 813 tests with 0 failures or errors (64 skipped).

I used AI-assisted review for edge-case analysis and verified the root cause, implementation, and tests locally.

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• I applied the project formatter/checkstyle without unrelated formatting changes.
• I added unit and integration tests.
• I added myself as author in every touched class.