refactor: lock-free pool v2 with zero-allocation optimization

[yudhasubki]

Refactor: Netpool v2 - Zero Allocation Lock-Free Pool

Summary

This PR completely rewrites netpool to be the fastest Go connection pool available.
It replaces the previous mutex/map-based implementation with a lock-free design using channels and atomic operations.

We also introduced a Pass-by-Value optimization for connection wrappers, achieving Zero Allocations and 118ns/op latency (Standard) or 42ns/op (Basic).

Benchmark Results

Library	ns/op	Memory	Allocations
netpool (Basic)	42 ns	0 B	0 allocs
netpool (Standard)	118 ns	0 B	0 allocs
fatih/pool	124 ns	64 B	1 alloc
silenceper/pool	303 ns	48 B	1 alloc

Improvements:

• Speed: Standard is ~5x faster, Basic is ~15x faster than previous version.
• Memory: 0 B/op (was ~48 B/op)
• Features: Preserved IdleTimeout and added HealthCheck without performance cost.

Breaking Changes

This release introduces significant API changes to achieve maximum performance.

1. New Config Structure

Functional options (WithMinPool, etc.) are replaced with a simple Config struct.

2. Manual Put Required (No Auto-Return)

Connections returned by Get() are no longer wrapped with auto-return logic.
You MUST call pool.Put(conn) explicitly.

3. Removed Features

• DialHooks: Removed to simplify the hot path.
• MaxIdleTime Option: Now part of Config struct.