Fix Rayleigh correction to use the same datatype as the input data

[pnuu]

This is workaround for the Pyspectral Rayleigh correction that always uses float64 datatype.

This includes also few additional dtype checks for other modifiers and enhancements. Those changes are here because I originally started this to hunt a data upcasting in true color composite, but didn't end up finding the final issue and didn't want to discard all the changes.

I'll create an issue to Pyspectral to fix the data upcasting. Hopefully tomorrow. Or a direct fix if I see a simple solution.

• [x] Tests added

[codecov[bot]]

Codecov Report

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

Project coverage is 96.09%. Comparing base (118fc93) to head (3f1076a). Report is 7 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2954 +/- ## ======================================= Coverage 96.09% 96.09% ======================================= Files 377 377 Lines 55110 55125 +15 ======================================= + Hits 52960 52975 +15 Misses 2150 2150 ``` | [Flag](https://app.codecov.io/gh/pytroll/satpy/pull/2954/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | Coverage Δ | | |---|---|---| | [behaviourtests](https://app.codecov.io/gh/pytroll/satpy/pull/2954/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `3.94% <0.00%> (-0.01%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/pytroll/satpy/pull/2954/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `96.19% <100.00%> (+<0.01%)` | :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=pytroll#carryforward-flags-in-the-pull-request-comment) to find out more.

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[coveralls]

Pull Request Test Coverage Report for Build 11517663375

Details

• 61 of 61 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 96.206%

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Totals
Change from base Build 11517264487:	0.003%
Covered Lines:	53219
Relevant Lines:	55318

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💛 - Coveralls

[djhoese]

@pnuu so is the plan for this to be closed and not used? Theoretically pyspectral should have all the changes for dtype stuff, right? Also I really thought I got pyspectral working and retaining dtypes. Shoot.

[pnuu]

Well, maybe the tests I've added should stay. I'll have a look at how much needs to be done to Pyspectral so that it doesn't upcast stuff, and whether there are still something that is needed on Satpy. Like a kwarg or something.

[pnuu]

I'm converting this to a draft while I inspect the Pyspectral side of things.

[pnuu]

Right. There was nothing wrong in Pyspectral, it was just the clipping of input value of reduce_strength that produced int64 for reduce_strength=1 and thus promoted the float32 data to float64.

[pnuu]

So in short: this PR makes sure the inputs to Rayleigh correction has proper data type to keep the data from being upcast. And adds the unrelated checks to other tests.

[mraspaud]

@djhoese do you want to look at this? otherwise it's good to merge