Without this change, `pyright` with `typeCheckingMode` set to `strict` reports:

```
error: Type of "fields" is partially unknown
    Type of "fields" is "MultiDict[Unknown, Unknown]" (reportUnknownVariableType)
```

when I use this method.

This should ensure that the tests work with Pytest 8 onwards. The
issue appears to be that __subclasses__ "returns a list of all those
references still alive." which could include the RequestRedirect. If
it does include RequestRedirect the tests will fail as it requires an
argument to be constructed. Note this test is not meant for
RequestRedirect.

Bug described at #2831

TypeErrors are now handled in the same manner as ValueErrors.

fixes #2842

Previously if a request had repeated slashes it could match a single
slash route and hence return a redirect response even if merge_slashes
was False.

Additionally setting the merge_slashes attribute of the map after
initialisation had no affect, compounding this problem.

This could happen for example with `min=0;max=500` as the `;` is not a
word character everything before it is ignored in the regex during the
finditer call. This then lefts the user confused as the `min=0;` was
silently ignored.

As this solves a publishing error.