fix(types): add missing argument to BeforeSend type definition

Goal

Correct type definition of BeforeSend. Fixes #428.

Updated type tests to verify BeforeSend type definitions against expected usage.

Fixes #428.

For the submitter, initial self-review:

[ ] Commented on code changes inline explain the reasoning behind the approach
[x] Reviewed the test cases added for completeness and possible points for discussion
[x] A changelog entry was added for the goal of this pull request
[x] Check the scope of the changeset - is everything in the diff required for the pull request?
This pull request is ready for:
- [ ] Initial review of the intended approach, not yet feature complete
- [ ] Structural review of the classes, functions, and properties modified
- [x] Final review

For the pull request reviewer(s), this changeset has been reviewed for:

[ ] Consistency across platforms for structures or concepts added or modified
[ ] Consistency between the changeset and the goal stated above
[ ] Internal consistency with the rest of the library - is there any overlap between existing interfaces and any which have been added?
[ ] Usage friction - is the proposed change in usage cumbersome or complicated?
[ ] Performance and complexity - are there any cases of unexpected O(n^3) when iterating, recursing, flat mapping, etc?
[ ] Concurrency concerns - if components are accessed asynchronously, what issues will arise
[ ] Thoroughness of added tests and any missing edge cases
[ ] Idiomatic use of the language