fix(configcheck): prevent memory leak by replacing time.After with time.NewTimer

[aa1ex]

Summary

• Fix memory leak in getCheckResult() caused by time.After() in select loop
• Add test demonstrating the leak and benchmarks comparing allocations

Problem

time.After() in a select loop creates a new timer on each iteration that won't be garbage collected until it fires. With frequent watch events, this causes ~280 bytes leak per event.

Solution

Replace time.After() with time.NewTimer() + Reset() pattern:

• Timer created once before the loop
• Reset after each event to preserve original timeout semantics
• Properly stopped on exit via defer

Benchmark Results

Pattern	Memory	Allocations
time.After() (before)	283 B/op	3 allocs/op
time.NewTimer (after)	0 B/op	0 allocs/op