fix: more robust tool call limit middleware (#33817)
* improving typing (covariance)
* adding in support for continuing w/ tool calls not yet at threshold,
switching default to continue
* moving all logic into after model
```py
ExitBehavior = Literal["continue", "error", "end"]
"""How to handle execution when tool call limits are exceeded.
- `"continue"`: Block exceeded tools with error messages, let other tools continue (default)
- `"error"`: Raise a `ToolCallLimitExceededError` exception
- `"end"`: Stop execution immediately, injecting a ToolMessage and an AI message
for the single tool call that exceeded the limit. Raises `NotImplementedError`
if there are multiple tool calls
"""
```
