Add MaxRequestBodySize enum to control request body capture with options:
- None: Don't capture request body (default)
- Small: Capture up to 1000 bytes
- Medium: Capture up to 10000 bytes
- Always: Capture entire body

Add max_request_body_size field to ClientOptions struct with default value of None

Add support for capturing request bodies in the Sentry middleware for Actix-Web.
This includes:
- Configurable request body size limits (Small/Medium/Always)
- Support for JSON and form-urlencoded content types
- Body capture and restoration logic to maintain request integrity
- Additional span data enrichment

Updates dependencies:
- Add serde_json, actix-http, futures dependencies

Implements a method to validate request body sizes against predefined limits:
- None: Don't capture request bodies (default)
- Small: Capture up to 1000 bytes
- Medium: Capture up to 10000 bytes
- Always: Capture entire body

- Add chunked transfer encoding check to prevent capturing chunked requests
- Add strict content-type validation for JSON and form-urlencoded
- Implement content length validation against size limits

Add new `Explicit(usize)` variant to `MaxRequestBodySize` enum, allowing users
to specify custom maximum request body size limits for event capture.

It's already handle by the is_within_size_limit.