BUG: Fix pd.read_html handling of rowspan in table header
- [x] closes #60210(Replace xxxx with the GitHub issue number)
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.

From the original thread:
```
s = '<table><tr><th rowspan="2">A</th><th>B</th></tr><tr><td>1</td></tr><tr><td>C</td><td>2</td></tr></table>'
buf = io.StringIO(s)
print(pd.read_html(buf)[0])
#    A                  B
#    A Unnamed: 1_level_1
# 0  1                NaN

# Expected:
#    A  B
# 0  A  1
# 1  C  2
```
The bug is due to rowspan > 1 in the header row which leads to overflow into the body rows. Current logic does not handle this case. I fix it by overflowing the partial rows from the header into the body (and similarly from body to footer if any).
Thanks @snitish 