Refactor connection handling and add SQL compatibility tests

[OutOfBedlam]

This pull request refactors database connection handling across the server codebase to centralize and standardize the use of pooled connections. The changes replace previous ad-hoc or context-specific connection acquisition with a new getPoolConn helper function, improving maintainability and consistency. Additionally, a new parallel HTTP query benchmark is introduced, and minor improvements are made to resource management.

Database Connection Refactoring:

• Added a new getPoolConn helper function in server.go to encapsulate pooled connection acquisition and wrapping, replacing repetitive connection logic throughout the codebase.
• Updated all HTTP and MQTT query/write handlers (http_query.go, http_write.go, mqtt_query.go) to use getPoolConn instead of previous connection methods, ensuring consistent pooled connection usage and error handling. [1] [2] [3] [4] [5]

Benchmarking and Resource Management:

• Added a new BenchmarkHTTPQueryParallel benchmark in http_test.go to measure parallel HTTP query performance under different database pool settings, aiding performance analysis and tuning.
• Ensured proper connection closure in the watcher initialization logic to prevent resource leaks.

Dependency Update:

• Updated the github.com/machbase/neo-client dependency in go.mod to a newer commit.

[codecov]

Codecov Report

❌ Patch coverage is 47.82609% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.47%. Comparing base (0513907) to head (4450c6f).

Files with missing lines	Patch %	Lines
mods/server/http_write.go	28.57%	5 Missing ⚠️
mods/server/server.go	55.55%	2 Missing and 2 partials ⚠️
mods/server/http_query.go	60.00%	1 Missing and 1 partial ⚠️
spi/watch.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #435   +/-   ##
=======================================
  Coverage   65.46%   65.47%           
=======================================
  Files         351      351           
  Lines       69730    69730           
=======================================
+ Hits        45652    45656    +4     
+ Misses      19228    19226    -2     
+ Partials     4850     4848    -2     

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