test(profiling): Extract shared profiler test cases into ContinuousProfilerTestCases.kt

Shared test logic (sampling, lifecycle, rate limiting, chunk restart,
close) is defined as extension functions on IContinuousProfiler in
ContinuousProfilerTestCases.kt. AndroidContinuousProfilerTest delegates
to these for common behavior while keeping legacy-specific tests inline.

This enables PerfettoContinuousProfilerTest to reuse the same test cases
with its own fixture.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 43jay