PERF: perf improvements in timedelta conversions from integer dtypes

```
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------
timedelta_convert                            |   0.2253 |  71.0374 |   0.0032 |
timedelta_convert_string_seconds             | 186.8856 | 184.1813 |   1.0147 |
timedelta_convert_string                     | 185.8193 | 181.2983 |   1.0249 |
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------

Ratio < 1.0 means the target commit is faster then the baseline.
Seed used: 1234

```

Using shortcuts for integers arrays