Parse only the query string for PaginatedList.totalCount (#3518)

`PaginatedList` computed `totalCount` with
`parse_qs(lastUrl)["page"][0]`, passing the whole URL to `parse_qs`.
`parse_qs` expects only a query string, so it splits the entire URL and
the first parameter's key ends up prefixed with the scheme/host/path.
This only worked because GitHub conventionally puts `page` last in the
`rel="last"` link. When `page` comes first (e.g.
`...?page=42&per_page=1`), `["page"]` raises `KeyError`.

The fix uses `Requester.get_parameters_of_url`, which extracts the query
string before `parse_qs` and is already used by the sibling pagination
code in the same file.

Added `testTotalCountWithLastPageAndPageFirst` with a replay fixture
whose `rel="last"` link lists `page` first. It raises `KeyError` on the
current code and passes with the change; the full
`tests/PaginatedList.py` suite passes.

Co-authored-by: Noethix55555 <277300782+Noethix55555@users.noreply.github.com>