feat: Adding a connection pool to reduce the time spent opening connection to Postgres

[Ma77Ball]

What changes were proposed in this PR?

This PR adds a HikariCP connection pool to SqlServer.scala so that jOOQ queries borrow pre-authenticated connections from a pool instead of opening a new TCP connection and performing SCRAM-SHA-256 authentication on every database call.

What changed in SqlServer.scala:

• Added a HikariConfig with maximumPoolSize=10, minimumIdle=2, connectionTimeout=30s, idleTimeout=10min, maxLifetime=30min (chosen to stay below typical PostgreSQL idle and load-balancer connection-reaping windows)
• Initialized a HikariDataSource and built the jOOQ DSLContext via DSL.using(dataSource, SQL_DIALECT) so queries draw from the pool
• Added a close() method to shut down the pool on application or test teardown, and updated clearInstance() to call it, so test classes that replace the singleton don't leak pool threads
• Added a documented warning against caching the DSLContext in a val or lazy val. MockTexeraDB swaps the singleton between test classes, and a cached context would hold a stale reference to a dead pool

Any related issues, documentation, discussions?

closes: #4852

How was this PR tested?

• Existing unit and integration tests pass — the pool-backed DSLContext is a drop-in replacement for the previous direct-driver context
• Verified the MockTexeraDB flow still works across test classes by running the full test suite and confirming no "Connection refused" failures from stale contexts

Was this PR authored or co-authored using generative AI tooling?

Co-authored with Claude opus 4.6 (Anthropic) in compliance with ASF

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 43.21%. Comparing base (deb0e2c) to head (dd50017).

Files with missing lines	Patch %	Lines
...c/main/scala/org/apache/texera/dao/SqlServer.scala	93.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4851      +/-   ##
============================================
+ Coverage     42.72%   43.21%   +0.49%     
+ Complexity     2185     1224     -961     
============================================
  Files          1031      764     -267     
  Lines         38152    30584    -7568     
  Branches       4004     2992    -1012     
============================================
- Hits          16301    13218    -3083     
+ Misses        20831    16692    -4139     
+ Partials       1020      674     -346     

Flag	Coverage Δ		*Carryforward flag
access-control-service	39.53% <ø> (ø)
agent-service	33.72% <ø> (ø)		Carriedforward from deb0e2c
amber	45.57% <93.33%> (+2.36%)	⬆️
computing-unit-managing-service	0.00% <ø> (ø)
config-service	0.00% <ø> (ø)
file-service	32.18% <ø> (ø)
frontend	33.08% <ø> (ø)		Carriedforward from deb0e2c
python	88.90% <ø> (ø)		Carriedforward from deb0e2c
workflow-compiling-service	47.72% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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[Yicong-Huang]

Looks good to me! Left inline comments

[Yicong-Huang]

please also change the title. this is not a refactor. we are adding a new feature.

[Yicong-Huang]

LGTM! Thanks

[Ma77Ball]

@Yicong-Huang, can you approve the workflows again?