Refactor `_resampled_scene()` and `_reduce_data()` methods of the `Scene` class

[pnuu]

This PR refactors Scene._resampled_scene() that @gerritholl reported to be complicated in https://github.com/pytroll/satpy/pull/3168#issuecomment-3109062005 . As there was a change to _reduce_data(), I did some additional refactoring to it too.

• [ ] Closes #xxxx
• [ ] Tests added
• [ ] Fully documented
• [ ] Add your name to AUTHORS.md if not there already

[codecov[bot]]

Codecov Report

:x: Patch coverage is 91.07143% with 5 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 96.28%. Comparing base (5cc91a2) to head (2d8d883). :warning: Report is 46 commits behind head on main.

Files with missing lines	Patch %	Lines
satpy/scene.py	91.07%	5 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3178      +/-   ##
==========================================
- Coverage   96.28%   96.28%   -0.01%     
==========================================
  Files         436      436              
  Lines       57830    57940     +110     
==========================================
+ Hits        55681    55785     +104     
- Misses       2149     2155       +6     

Flag	Coverage Δ
behaviourtests	3.78% <17.85%> (+<0.01%)	:arrow_up:
unittests	96.37% <91.07%> (-0.01%)	:arrow_down:

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[pnuu]

I'll do some more refactoring to _reduce_data().

[coveralls]

Pull Request Test Coverage Report for Build 16566762203

Details

• 51 of 56 (91.07%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.381%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
satpy/scene.py	51	56	91.07%
<!--	Total:	51	56

Totals
Change from base Build 16528353281:	0.0%
Covered Lines:	56082
Relevant Lines:	58188

---

💛 - Coveralls

[gerritholl]

Thanks! I've merged this into #3168 but there is still an issue with missing test coverage.