feat(pool): Improve success rate of new connections

[cyningsun]

Description

This PR continues the work from the previously closed PR (based on #3418), which was automatically closed after its base branch was merged.

It implements a context pattern for connection creation to prevent premature cancellation caused by short-lived request timeouts, which previously led to connection pool instability under high concurrency.

Solution

• Implemented a context approach for connection creation, similar to database/sql and net/http. The dialing operation now uses an independent context with a reasonable DialTimeout, while still listening for cancellation from the original request context for efficient cleanup
• Queue-based Fairness: Used a FIFO queue to ensure fairness among waiters when sharing a successful connection, preventing starvation.

Changes

1. Implemented a FIFO queue for connection sharing.
2. Introduced a dedicated putIdleConn method to handle placement of newly created connections into the pool, bypassing the Put method’s hooks and idle connection checks.

• Avoids unnecessary hook executions for newly established connections, improving performance and reducing overhead.
• Preserves resources by circumventing the MaxIdleConns constraint during initial connection placement, preventing valid connections from being discarded prematurely when p.idleConnsLen.Load() >= p.cfg.MaxIdleConns.
• Defers enforcement of MaxIdleConns limits to the existing check during subsequent Put operations, rather than immediately rejecting newly created connections. ( Avoids impacting connection acquisition latency by not adding cleanup overhead to popIdle)

References

• Closes Proposal: Align context handling for connection creation with database/sql and net/http #3497
• Discussion with @ndyakov in Feat/improve success rate of new connections #3502 Feat/improve success rate of new connections #3508

[ndyakov]

@cyningsun thank you for opening this pr, looking forward to continuing the discussion.

[ndyakov]

@cyningsun Thank you for this contribution. I do think we can include it in the library, I do not see any issues with it at the moment.

[ndyakov]

@cyningsun left a question regarding the pool balance, the rest looks good.

[cyningsun]

@ndyakov My apologies for the delayed response. The PR is now updated and ready for your next review.

[ndyakov]

Looks good to me, I am working on something related to the semaphore, let's merge this and I will try to resolve the conflicts on my end.

[htemelski-redis]

Looks good to me too