fix: fix tdim issue

[jamesrafe]

Closes #44

Fix one-dimensional FITS TDIM values such as TDIM=(3). These were parsed as an integer, but BinaryField expects dimensions as a tuple or nothing. The new helper normalizes them to (3,) across all binary-table construction paths and adds tests for the changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.68%. Comparing base (870e4ee) to head (c00fcc3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
+ Coverage   46.35%   46.68%   +0.33%     
==========================================
  Files          17       17              
  Lines        2550     2551       +1     
==========================================
+ Hits         1182     1191       +9     
+ Misses       1368     1360       -8     

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[barrettp]

1. Remove prepended underscore, i.e., _parse_tdim() -> parse_tdim(),
2. The argument string should not require the strip() function. If it does, then there is a problem with the initial string parsing function or regex,
3. Suggest parsing the string using a Regex to ensure that the Tuple values are integers, instead of eval() or using a replace() to insert the missing comma,
4. The function should return a Tuple or nothing, where nothing means that TDIMj is either missing or an empty string, and
5. The function should be more concise, i.e., no more that 1 or 2 lines of code.

Note that the TDIMj Tuple also needs to be reconciled with the array size and element type. For example, if the element type is a string then, the TDIMj should return a Tuple of one fewer dimensions, because the first dimension gives the size of the string. See the FITS standards document for details.

[jamesrafe]

Hi @barrettp, parse_tdim now uses regex, returns nothing for missing/empty values, and handles FITS header padding without strip. Tests also cover one-dimensional and multi-dimensional values plus invalid input. Thank you!