Fixed timestamp to datetime conversion for values with fractional seconds before the epoch

[alexander-beedie]

The timestamp_XX_to_datetime functions all panic with "invalid or out-of-range datetime" on conversions of values with fractional seconds before the epoch (where the timestamp becomes negative).

For these timestamps (pre-epoch, fractional secs) the (v % <scale_factor>) as u32 formulation is not valid, as

• the result is a negative number
• ... which causes integer wraparound via as u32
• ... which then leads to a panic, as we can't init with billions of microseconds (for example).

This PR allows pre-epoch conversions with fractional seconds to be handled correctly, and adds some new tests to provide the missing coverage.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 :tada:

Comparison is base (e14c238) 83.92% compared to head (888f780) 83.94%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1467 +/- ## ========================================== + Coverage 83.92% 83.94% +0.01% ========================================== Files 387 387 Lines 41605 41620 +15 ========================================== + Hits 34917 34936 +19 + Misses 6688 6684 -4 ``` | [Impacted Files](https://codecov.io/gh/jorgecarleitao/arrow2/pull/1467?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao) | Coverage Δ | | |---|---|---| | [src/temporal\_conversions.rs](https://codecov.io/gh/jorgecarleitao/arrow2/pull/1467?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao#diff-c3JjL3RlbXBvcmFsX2NvbnZlcnNpb25zLnJz) | `91.39% <100.00%> (+0.44%)` | :arrow_up: | ... and [4 files with indirect coverage changes](https://codecov.io/gh/jorgecarleitao/arrow2/pull/1467/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao)

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[ritchie46]

Thanks @alexander-beedie. Great fix. :+1: