Add limit param for list items

[philippemoro]

Summary

This pull request introduces support for explicitly passing the limit parameter, as described in the Rollbar API documentation.

Testing
It appears that some of the token limit issues reported in rollbar/rollbar-mcp-server#42
may have been caused by requests using a higher-than-intended default limit value.
According to the documentation, the intended default is 20. When explicitly setting limit:20, the response size (and number of tokens) was significantly reduced

[brianr]

Thank you!

Just a note on the docs - the doc you linked is for a different endpoint, for fetching instances (called Occurrences in the UI). This tool is for getting items. For items, the default is 100 per page. In any case, exposing the limit param and defaulting it to 20 makes sense.

[brianr]

Merged these changes in #59. Thanks again!