Draft: Optimize to_timestamp

[vojtechtoman]

Which issue does this PR close?

Closes #9090.

What changes are included in this PR?

This is still work in progress. The PR introduces a few simple optimizations to to_timestamp (without format). On my local machine, the performance improvement in the benchmarks is about 15%.

Are these changes tested?

Yes, existing unit tests and benchmarks.

Are there any user-facing changes?

No.

[tustvold]

I wonder if this could make use of the upstream parsers that are already highly optimised

https://docs.rs/arrow-cast/latest/arrow_cast/parse/index.html

[vojtechtoman]

@tustvold the existing implementation was already using those (via string_to_timestamp_nanos). One thing I noticed early on while profiling is that the upstream parser can be optimized even further. This is why I copied a bunch of parsing code from upstream to this PR to see if there are any quick wins there (there are). Obviously, this should go into upstream eventually.

[tustvold]

Heh, I thought the code looked familiar. Perhaps we could work on this upstream to avoid a load of duplicated code and make it more obvious what has changed?

[vojtechtoman]

@tustvold Shall I open an issue in arrow-rs then?

[tustvold]

Or just file a PR tbh, minor changes don't need issues

[vojtechtoman]

@tustvold I have created apache/arrow-rs#5542

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