feat(python): Allow loading data from multiple Excel/ODS workbooks and worksheets

[alexander-beedie]

Extends the recent #20404 update, allowing loading from multiple worksheets while loading from multiple workbooks, following discussion here: #20404 (comment).

(Currently can load one worksheet from multiple workbooks, or multiple worksheets from one workbook - this enables both options at the same time).

Example

pl.read_excel(
    "/path/to/multiple/workbooks/**/data*.xlsx",
    sheet_name=["sheet1","sheet2","sheet3"],
)

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 78.98%. Comparing base (a6fffd4) to head (5575f4b).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/io/spreadsheet/functions.py	83.33%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20465      +/-   ##
==========================================
- Coverage   79.00%   78.98%   -0.02%     
==========================================
  Files        1563     1563              
  Lines      220449   220566     +117     
  Branches     2488     2490       +2     
==========================================
+ Hits       174157   174209      +52     
- Misses      45719    45784      +65     
  Partials      573      573              

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