fix(hedge): assert non-zero rotation period on construction

[Alpy16]

Description

This PR addresses an issue where Hedge::new and Hedge::new_with_mock_latencies accept a Duration::ZERO rotation period during configuration. This behavior subsequently causes an unrecoverable integer divide-by-zero panic in RotatingHistogram::maybe_rotate upon the first request invocation.

By validating the period parameter at the API boundary via an explicit assertion, this change ensures that invalid configurations fail-fast during initialization rather than causing runtime instability.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Proposed Changes

• Added assert!(period > Duration::ZERO, ...) to Hedge::new.
• Added an identical guard to Hedge::new_with_mock_latencies to protect immediate history pre-population logic.
• Added synchronous regression tests to the hedge integration test suite covering both constructors.

Verification Run

Executed the module integration tests locally across the workspace using:

cargo test --package tower --all-features

All 7 tests within tests/hedge/main.rs passed successfully alongside the rest of the workspace and doc-test suite.

Closes #862