Move stitching out of legacy scaling_factors/ to avoid confusion

[backmari]

Description of work:

Some cleanup:

• The modules in the folder scaling_factors/ are unrelated to stitching scaling factors. To avoid confusion, move the stitching functions into a separate module stitching.py. (This was suggested by @welbournR.)
• Move all tests into either tests/unit/ or tests/integration/.
• Remove the __all__ variable since wildcard imports are not recommended.

Check all that apply:

• updated documentation
• Source added/refactored
• Added unit tests
• Added integration tests
• Verified that tests requiring the /SNS and /HFIR filesystems pass without fail

References:

• Links to IBM EWM items:
• Links to related issues or pull requests:

⚠️ Manual test for the reviewer

(Instructions for testing here)

Check list for the reviewer

• best software practices
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.15%. Comparing base (3ce9476) to head (03cf89b).

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #115      +/-   ##
==========================================
- Coverage   85.16%   85.15%   -0.02%     
==========================================
  Files          23       22       -1     
  Lines        2925     2923       -2     
==========================================
- Hits         2491     2489       -2     
  Misses        434      434              

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[ktactac]

PR simply renames stitching files without trouble