[matthew-walters]

Fixes #1051.

With the profiler feature enabled, pipeline timers called Instant::now() even after Counters::disable(). The enabled flag guarded the counter helper methods, but several pipeline stages accessed their timers directly.

Timers now track whether they are disabled. Counters::enable() and disable() update every timer, and Counters::reset() synchronizes timer state for compatibility with callers that modify the public enabled field directly. Disabling a running timer discards its open interval, so time spent disabled is not charged after re-enabling.

The CCD time-of-impact timer now resumes for each internal clamp pass instead of restarting. Because Counters::reset() clears it at the beginning of the outer step, it now accumulates timing across all CCD substeps.

The regressions verify that:

• direct timer operations are inert while counters are disabled
• disabling and re-enabling does not include the disabled interval
• direct changes to Counters::enabled take effect on the next pipeline step
• CCD timing includes injected work from multiple clamp passes

All three new regressions fail on the unpatched upstream revision and pass with this change.

Validation:

• cargo test -p rapier3d --features profiler --test pipeline_counters
• cargo test -p rapier3d --test pipeline_counters
• cargo test -p rapier2d --features profiler --lib
• RUSTFLAGS="-D warnings" cargo clippy -p rapier2d -p rapier3d --features profiler
• RUSTFLAGS="-D warnings" cargo clippy -p rapier3d --features profiler --test pipeline_counters
• cargo fmt --all -- --check
• git diff --check