Improve msd_type parsing: add whitespace handling, type validation, and missing tests

[tanii1125]

Summary

EinsteinMSD currently lowercases the msd_type string but does not handle leading/trailing whitespace or non-string inputs. This leads to errors such as:

• msd_type=" xy " → ValueError instead of working as "xy"
• msd_type=123 → AttributeError ("int has no attribute 'lower'")

Proposed improvements

1. Add .strip() before .lower() to handle inputs like " xy ".
2. Add type validation (raise TypeError when msd_type is not a string).
3. Add new tests to cover:
   • whitespace (" xy ")
   • uppercase/mixed case (" Xz ")
   • non-string inputs

Why this is beneficial

• Makes msd_type parsing more robust.
• In line with how MDAnalysis handles flexible string inputs.
• Increases test coverage for the analysis module.

I am willing to submit a PR.

[Sparshagarwal29]

I am interested in working on this issue as well. Is this issue assigned to anyone ? If not, I’d be happy to take it !!

[mariam-29]

I want to work on this issue can you assign it to me?

[anujaiitj123]

I would like to work on this issue. Could you please assign it to me.

[dibyajyoti-mandal]

Is this open to work on? I'd like to work on it.