Optimize sqlparse.utils.imt().

[adamchainz]

Thanks for contributing!

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Profiling a sqlparse.parse() on a bunch of large SELECT queries, 14ms out of 59ms, or ~24% of the time, was spent in sqlparse.utils.imt().

Looking at that function, it did some moving of the m and t parameters into lists, wasting work when they’re not set or a single element which can use a faster check. To mitigate this, I optimized it to do the check only when the parameters are set, and avoid the listification of single elements.

This doubled its speed, saving 7ms in the same profile.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 85.71429% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 96.92%. Comparing base (60486b9) to head (e7eab4c).

Files	Patch %	Lines
sqlparse/utils.py	85.71%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #766 +/- ## ========================================== - Coverage 97.04% 96.92% -0.12% ========================================== Files 20 20 Lines 1558 1563 +5 ========================================== + Hits 1512 1515 +3 - Misses 46 48 +2 ```

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[andialbrecht]

Thanks for the patch! That makes the code much more readable as well.