fix(testing): honor history reverse order

[mahayash315]

Summary

• parse the ReverseOrder query parameter in the testing WebServer
• forward the parsed value to get_execution_history
• cover omitted, false, and true values with a regression test

Root cause

The WebServer handler hard-coded reverse_order=False, even though the executor already supports reverse-order history and pagination.

Testing

• hatch run dev-testing:test (1,365 passed)
• hatch run dev-testing:typecheck
• hatch fmt --check
• focused history-handler tests (8 passed)

Fixes #594

[yaythomas]

thank you so much @mahayash315, great contribution, welcome to dex!

Verified the wire contract against the public Lambda API model: ReverseOrder querystring name, lowercase true/false serialization from boto3, and absent-defaults-to-false all match the service exactly.

just waiting for CI to clear.