Fix native resampler not working for some chunk sizes

[djhoese]

This PR fixes the issue described in #2245 where a user's chosen chunk size for their data may not be divisible by the aggregation factor, but the overall shape of the array is. There is no reason except avoiding rechunking that this shouldn't work. This PR makes it so rechunking is done if needed.

I also removed the unnecessary rechunking done in the replication step. My hope is that dask will figure out this rechunking automatically and that this won't be needed.

@simonrp84 any testing you can do would be greatly appreciated.

• Closes native resampler fails for some chunk sizes #2245
• Tests added

[codecov]

Codecov Report

Merging #2291 (95a1f35) into main (402804f) will decrease coverage by 0.00%.
The diff coverage is 99.04%.

@@            Coverage Diff             @@
##             main    #2291      +/-   ##
==========================================
- Coverage   94.32%   94.31%   -0.01%     
==========================================
  Files         308      308              
  Lines       46169    46161       -8     
==========================================
- Hits        43547    43539       -8     
  Misses       2622     2622              

Flag	Coverage Δ
behaviourtests	4.62% <8.57%> (+0.01%)	⬆️
unittests	94.95% <99.04%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/resample.py	79.96% <97.82%> (+0.40%)	⬆️
satpy/tests/test_resample.py	88.90% <100.00%> (-0.37%)	⬇️

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[coveralls]

Coverage decreased (-0.0009%) to 94.907% when pulling 95a1f35 on djhoese:bugfix-native-agg-chunks into 402804f on pytroll:main.

[mraspaud]

LGTM, thanks for also migrating to pytest!