Cache columeToIndexFieldMap

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.02%. Comparing base (041a992) to head (aaeacbd).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #131 +/- ## ========================================== + Coverage 80.72% 81.02% +0.30% ========================================== Files 5 5 Lines 555 564 +9 ========================================== + Hits 448 457 +9 Misses 92 92 Partials 15 15 ``` | [Flag](https://app.codecov.io/gh/georgysavva/scany/pull/131/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Georgy+Savva) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/georgysavva/scany/pull/131/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Georgy+Savva) | `81.02% <100.00%> (+0.30%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Georgy+Savva#carryforward-flags-in-the-pull-request-comment) to find out more.

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[georgysavva]

This looks great, thank you. This PR fixes https://github.com/georgysavva/scany/issues/25.

[georgysavva]

@zolstein here is the new release: https://github.com/georgysavva/scany/releases/tag/v2.1.2