Better handling of footnotes in columns

[prakaa]

Current handling of footnotes in column names could be improved.

At the moment, it's a one line regex:

isp-workbook-parser/src/isp_workbook_parser/read_table.py

Line 75 in 8f1a006

columns = columns.str.replace(r"(?<=[^\s\d])\d$", "", regex=True)

This has some issues:

1. Stripping 3 from Phase 3 as below (expected_closure_years)

2. Foonote with space before isn't stripped (locational_cost_factors)