Uses a memory pool for parser struct and format []byte
Uses a new go 1.20 feature to avoid allocations for []byte to string conversions in allowable cases.
go 1.20 also fixes a go bug for parsing fractional sec after a comma, so we can eliminate a workaround.
The remaining allocations are mostly unavoidable (e.g., time.Parse constructing a FixedZone location or part to strings.ToLower).
Results show an 89% reduction in allocated bytes for the big benchmark cases, and for some formats an allocation can be avoided entirely.
There is also a resulting 26% speedup in ns/op.
Details:
BEFORE:
cpu: 12th Gen Intel(R) Core(TM) i7-1255U
BenchmarkShotgunParse-12 19448 B/op 474 allocs/op
BenchmarkParseAny-12 4736 B/op 42 allocs/op
BenchmarkBigShotgunParse-12 1075049 B/op 24106 allocs/op
BenchmarkBigParseAny-12 241422 B/op 2916 allocs/op
BenchmarkBigParseIn-12 244195 B/op 2984 allocs/op
BenchmarkBigParseRetryAmbiguous-12 260751 B/op 3715 allocs/op
BenchmarkShotgunParseErrors-12 67080 B/op 1679 allocs/op
BenchmarkParseAnyErrors-12 15903 B/op 200 allocs/op
AFTER:
BenchmarkShotgunParse-12 19448 B/op 474 allocs/op
BenchmarkParseAny-12 48 B/op 2 allocs/op
BenchmarkBigShotgunParse-12 1075049 B/op 24106 allocs/op
BenchmarkBigParseAny-12 25394 B/op 824 allocs/op
BenchmarkBigParseIn-12 28165 B/op 892 allocs/op
BenchmarkBigParseRetryAmbiguous-12 37880 B/op 1502 allocs/op
BenchmarkShotgunParseErrors-12 67080 B/op 1679 allocs/op
BenchmarkParseAnyErrors-12 3851 B/op 117 allocs/op
