ENH: Improved error message and raise new error for small-string NaN edge case in HDFStore.append
Updated **pytables.py** to improve error messages caused by datatype mismatches in **HDFStore.append**. Also added **ValueError** for when the NaN representation cannot fit into the column. Modified tests concerning the improved error message and added new test for when column is type string with length <3 and as such **nan_rep** 'nan' is too big.

- [ ] closes #16300
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests)
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
I've removed the comments mentioned and reverted the error type. I've replaced the test with a function of 3 tests testing the following cases:

- Error on string column too small
- Error on modified nan_rep too big
- Success on small modified nan_rep in small string column

There may be some odd git stuff during me updating the main branch due to my unfamiliarity with the GitHub contribution workflow and git as a whole. Thanks @JakeTT404  This impacted #60795 - https://github.com/pandas-dev/pandas/pull/60795#discussion_r1943799181

Is this okay to backport to 2.3? Yup sure OK with me Backport PR: #60907