performance(chrono): use write! macro to improve date formatting

[fvaleye]

Description

Replace formatter-based string construction with manual formatting using String::with_capacity and write! across chrono ToSql implementations. This reduces allocations and formatter overhead on hot paths.

Local benchmark with my laptop

Type	Before (format)	After (write + capacity)	Speedup	Improvement
NaiveDate::to_sql	112.9 ns	53.6 ns	2.11x	111% faster
NaiveTime::to_sql	174.1 ns	119.0 ns	1.46x	46% faster
NaiveDateTime::to_sql	229.1 ns	154.0 ns	1.49x	49% faster