docs: correct the _perf path references after the bench moved

The `_perf/` measurement bench was gitignored and had never been committed, so
23 of the 27 scripts cited by the perf documents were already lost. The 11
surviving files (4 scripts, cfg_dm1.json, 5 result JSONs, the 53 MB MJPG clip)
have been moved to D:\orisys_ws\docs\performance\perf-measurements\ and the
scripts patched to resolve their defaults next to themselves. The directory has
been removed from this repo.

These three files said the scripts were deleted, which was only half true:
they are moved, and the four surviving ones still run. Repointed:

- src/orisys/sensor.py: the FILTER_PRESETS comment now names the real location
  (comment only; FILTER_PRESETS itself is unchanged).
- docs/filters.md and examples/filters/README.md: the same correction for the
  latency/noise measurement provenance.

No behaviour change.

src/orisys/sensor.py

@@ -57,7 +57,8 @@ DEFAULT_FLOW_EMA_ALPHA = 1.0
 #: write ``"filters": {"preset": "balanced"}`` and override any single key on
 #: top of it; the resolved values are what ``Sensor.filters_state()`` reports.
 #: The latency/noise trade-offs behind these numbers are measured in
-#: ``_perf/`` and tabulated in ``docs/filters.md``.
+#: ``docs/performance/perf-measurements/`` (moved out of the once-gitignored
+#: ``orisys-sdk/_perf/`` on 2026-09-27) and tabulated in ``docs/filters.md``.
 FILTER_PRESETS = {
     # Everything off: the file says what runs, and the raw reading is the record.
     "off": {