Is your feature request related to a problem? Please describe.

For repeated measurement cycles (start/stop/extract/clear in a loop), Coverage.erase() is the only reliable reset API on Coverage itself. But erase() sets _inited_for_start = False, so the next start() reruns _init_for_start(), rebuilding Core, Collector, InOrOut, creating a new CoverageData, and registering cleanup handlers again.

In our case (a fuzzer collecting branch/arc coverage thousands of times in no_disk mode), this repeated re-initialization is overhead: tracing configuration does not change between cycles, only collected data does.

Note: this request is not about keeping per-thread tracer instances alive across start()/stop(); Collector.start() recreates tracer instances each time by design.

Describe the solution you'd like

A public method like Coverage.clear_data() that:

• Clears collected coverage data (SQLite rows / in-memory state)
• Keeps existing Core/Collector/InOrOut wiring intact for the next start()
• Does not set _inited_for_start = False
• Avoids repeated cleanup-handler registration for every cycle

Usage would be:

cov = coverage.Coverage(branch=True, data_file=None, config_file=False)

for i in range(10000):
    cov.start()
    do_work()
    cov.stop()
    data = cov.get_data()
    # ... extract arcs/lines from data ...
    cov.clear_data()  # clear data, keep start-time initialization

Describe alternatives you've considered

1. Calling Coverage.erase() each cycle — functionally works, but reruns _init_for_start() each iteration. In no_disk mode it also accumulates CoverageData/SQLite objects until process shutdown, because old data objects are retained for _atexit force-close.

Additional context

Our use case is a fuzzer that reuses one Coverage instance across thousands of iterations in no_disk mode during compilation. Each iteration compiles different code and we extract arcs, so we need a clean slate each cycle. Include/exclude rules, branch mode, and other tracing configuration are fixed; only coverage data should reset.