Replace placeholder tests and run every integration suite in CI

Problem

Several test files contain only placeholder assertions such as expect(true), including the runner, suite, reporter, CLI, and filter tests. In addition, the default zig build test step does not execute the dedicated hooks, comprehensive mock, snapshot, or time test executables.

This allows regressions in core behavior to pass CI.

Proposed work

• Replace placeholder tests with behavioral tests for the corresponding modules.
• Make the default test step execute hooks, mock, snapshot, and time integration suites.
• Ensure CI runs the complete default test step.
• Include all maintained examples in the examples step or document why an example is compile-only.

Acceptance criteria

• No placeholder-only test files remain.
• zig build test runs all core and integration tests.
• A deliberate failure in any dedicated suite fails CI.
• Generated snapshots and coverage artifacts do not dirty the working tree unexpectedly.