Fix Blockwise vmap dispatch for no batch dimensions

[cetagostini]

Description

Updates comments in funcify_Blockwise to avoid confusion about behaviour. Adds tests to verify correct behavior for these cases.

Related Issue

• Closes #
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

[ricardoV94]

Maybe all was good and PR isn't needed. @jessegrabowski do you have a snippet where things were failing without batch dims? It was from the linalg PR right?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.70%. Comparing base (f83c05b) to head (36faee4).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1705      +/-   ##
==========================================
+ Coverage   81.68%   81.70%   +0.02%     
==========================================
  Files         244      246       +2     
  Lines       53549    53632      +83     
  Branches     9433     9438       +5     
==========================================
+ Hits        43741    43822      +81     
- Misses       7328     7329       +1     
- Partials     2480     2481       +1     

Files with missing lines	Coverage Δ
pytensor/link/mlx/dispatch/blockwise.py	85.71% <ø> (+19.04%)	⬆️

... and 3 files with indirect coverage changes

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