fix: allow EVALSHA in ClusterPipeline (#2914)

[ahmed5145]

Description of change

Fixes #2914

EVALSHA was listed in PIPELINE_BLOCKED_COMMANDS, so ClusterPipeline.evalsha() always raised even though RedisCluster.determine_slot() already routes EVAL/EVALSHA by keys (including the 0-key random-slot case).

This removes EVALSHA from the blocked list so cluster pipelines can queue EVALSHA like other keyed commands. Callers must still:

• load the script on the target node(s) first (e.g. cluster SCRIPT LOAD, which loads on all primaries)
• keep all script keys on the same hash slot

Also updates docs/lua_scripting.rst and adds regression coverage:

• mock tests that EVALSHA is no longer blocked and can be queued on ClusterPipeline
• a cluster integration test (test_evalsha_in_pipeline) for CI with a live cluster

Pull Request check-list

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?

---

Note

Medium Risk
Changes cluster pipeline command routing and transactional slot logic for EVAL/EVALSHA; risk is moderate but bounded by extensive tests and narrow scope (EVALSHA only, not full scripting on pipelines).

Overview
Enables EVALSHA on cluster pipelines by removing it from PIPELINE_BLOCKED_COMMANDS, so queued scripts route like other keyed commands instead of raising immediately.

Pipeline routing treats EVAL/EVALSHA without calling COMMAND GETKEYS when numkeys is 0 (avoids Redis <7 breakage). Transactional pipelines get _resolve_transaction_slot: zero-key scripts reuse an existing transaction slot or pick one at random; keyed commands can retarget away from a slot chosen only by prior zero-key scripts.

Docs in lua_scripting.rst describe cluster pipeline EVALSHA behavior and limits (EVAL, load_scripts, etc. still unsupported on cluster pipelines). Sync/async unit and integration tests cover blocking removal, zero-key execute, and transaction slot reuse.

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