esp-hal Fix systimer timestamp conversion

Perf improvement, improved systimer accuracy on 26MHz C2, one step towards removing Clocks, what else do we need? (a way to do all this without taking a critical section to read frequencies).

This PR replaces the old assumption that the systimer counter divides evenly into microseconds with a bit of precomputation that ensures precision. The PR also introduces an optimized method for the more common cases, where the end result can be obtained by shifting instead of 64-bit integer division.

Dec 08 '25 18:12 bugadani

/hil full

Dec 10 '25 16:12 bugadani

Triggered full HIL run for #4634.

Run: https://github.com/esp-rs/esp-hal/actions/runs/20106494606

Status update: ❌ HIL (full) run failed (conclusion: failure).

Dec 10 '25 16:12 github-actions[bot]

/hil full

Dec 15 '25 19:12 bugadani

Triggered full HIL run for #4634.

Run: https://github.com/esp-rs/esp-hal/actions/runs/20245654039

Status update: ❌ HIL (full) run failed (conclusion: failure).

Dec 15 '25 20:12 github-actions[bot]

/hil esp32

I want to see if that hang reproduces today

Dec 16 '25 08:12 bugadani

Triggered HIL run for #4634 (chips: esp32).

Run: https://github.com/esp-rs/esp-hal/actions/runs/20260954095

Status update: ✅ HIL (per-chip) run succeeded.

Dec 16 '25 08:12 github-actions[bot]