Fix engine crash on module client blocking during keyspace events

[yairgott]

This change enhances user experience and consistency by allowing a module to block a client on keyspace event notifications. Consistency is improved by allowing that reads after writes on the same connection yield expected results. For example, in ValkeySearch, mutations processed earlier on the same connection will be available for search.

The implementation extends VM_BlockClient to support blocking clients on keyspace event notifications. Internal clients, LUA clients, clients issueing multi exec and those with the deny_blocking flag set are not blocked. Once blocked, a client’s reply is withheld until it is explicitly unblocked.

[codecov]

Codecov Report

Attention: Patch coverage is 59.22330% with 42 lines in your changes missing coverage. Please review.

Project coverage is 70.98%. Comparing base (3f6581b) to head (042b54e).
Report is 29 commits behind head on unstable.

Files with missing lines	Patch %	Lines
src/module.c	0.00%	29 Missing ⚠️
src/networking.c	51.85%	13 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1819      +/-   ##
============================================
- Coverage     70.99%   70.98%   -0.01%     
============================================
  Files           123      123              
  Lines         65651    65728      +77     
============================================
+ Hits          46609    46660      +51     
- Misses        19042    19068      +26     

Files with missing lines	Coverage Δ
src/expire.c	96.59% <100.00%> (ø)
src/server.h	100.00% <ø> (ø)
src/t_hash.c	96.37% <100.00%> (+0.13%)	⬆️
src/t_list.c	92.84% <100.00%> (+0.28%)	⬆️
src/t_set.c	97.84% <100.00%> (ø)
src/t_stream.c	93.17% <100.00%> (+0.60%)	⬆️
src/t_zset.c	96.89% <100.00%> (+0.04%)	⬆️
src/networking.c	88.38% <51.85%> (-0.52%)	⬇️
src/module.c	9.56% <0.00%> (-0.06%)	⬇️

... and 17 files with indirect coverage changes

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[madolson]

Ok, I'm aligned with the design now. Just some other misc comments.

[madolson]

@valkey-io/core-team This API is a bit late to be added. The feature adds a new functionality to using keyspace notifications, allowing them to block clients. The goal is to provide read and after write consistency for the VSS module.

There are two different ways to provide this guarantee, either block the write until it's visible in the index or block the read until all pending writes were ingested. The search module preferred to use the blocking of the write approach, but need an API to block the writes.

@murphyjacob4 Will follow up to see if there is a away to avoid this new functionality.

[QuChen88]

Note: this PR is mainly fixing an engine crash and read after write consistency on the same connection related to the VSS module, so it is technically a bug fix in my mind, not new feature.

Also with the latest revision, the module API change is kept to minimal.

[zuiderkwast]

I didn't review the test case yet. It's failing though in the latest CI run:

*** [err]: Event that fires twice in tests/unit/moduleapi/block_keyspace_notification.tcl
Rename event not propagated within 5 seconds

Please look into it. We've had many problems with flaky test.

[QuChen88]

With the simplified module API code, I will take another look this week on the functional change in module.c. Will give my thumb-up if all looks good.