Fix add_transformations broken state after invalid input

[harshitgajjela-droid]

Fixes #2558

Changes made in this Pull Request:

• Added input validation in add_transformations to raise TypeError if any transformation is not callable, preventing broken trajectory state
• Added test test_add_transformations_rejects_non_callable in testsuite/MDAnalysisTests/coordinates/base.py

LLMs or other AI-powered tools (beyond simple IDE use cases) were used in this contribution: no

• Issue raised/referenced?
• Tests updated/added?
• Documentation updated/added?
• package/CHANGELOG file updated?
• Is your name in package/AUTHORS?
• LLM/AI disclosure was updated.

I certify that I can submit this code contribution as described in the Developer Certificate of Origin, under the MDAnalysis LICENSE.

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📚 Documentation preview 📚: https://mdanalysis--5265.org.readthedocs.build/en/5265/

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 84.37500% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.15%. Comparing base (900d20b) to head (ae06e95).

Files with missing lines	Patch %	Lines
package/MDAnalysis/coordinates/base.py	84.37%	6 Missing and 4 partials ⚠️

❗ There is a different number of reports uploaded between BASE (900d20b) and HEAD (ae06e95). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (900d20b)	HEAD (ae06e95)
	5	2

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5265      +/-   ##
===========================================
- Coverage    93.83%   86.15%   -7.69%     
===========================================
  Files          180      180              
  Lines        22473    22476       +3     
  Branches      3189     3191       +2     
===========================================
- Hits         21088    19364    -1724     
- Misses         923     2658    +1735     
+ Partials       462      454       -8     

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