snapshots: measure SELECT / READ commands and show timing stats

Server measures every classified APDU (A4 select, B0 read binary, B2 read
record) from command to response: _collect_apdu_times() enables the tracer
(reattaching it if pySim nulled it) and /api/select + /api/read return
'apdu_times': [{type, ms}]. Collection is safe: handlers hold _CARD_LOCK.

Snapshots store per-file {select_ms, read_ms}, a ms value per record and
snapshot-level stats {select, read_binary, read_record}: {min, max, avg,
count} plus total_ms (wall time of the scan). The snapshot view gets a
summary under the title (files/records counts, scan time, min/avg/max per
command type) and shows select/read per file and read time per record.
Timings are display-only: checks, snapshots comparison and imports ignore
them (old snapshots simply show 'No timing data').

Tests: Python classifier/collection (tests/test_apdu_timing.py) and
frontend stats/accumulator/format/build-file/summary. SW cache v99 ->
v100; help, README and docs/api.md updated.

tests/test_apdu_timing.py

@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+"""Tests for per-command APDU timing collection (card snapshot measurements)."""
+
+import sys
+import time
+import types
+import unittest
+from pathlib import Path
+from unittest import mock
+
+PROJECTS = Path(__file__).resolve().parents[2]
+PY_SIM = PROJECTS / 'pysim'
+if str(PY_SIM) not in sys.path:
+    sys.path.insert(0, str(PY_SIM))
+
+import pysim_otaman_server.server as S
+
+
+class TestClassifyApdu(unittest.TestCase):
+    def test_select(self):
+        self.assertEqual(S._classify_apdu('00a40004023f0000'), 'select')
+
+    def test_read_binary(self):
+        self.assertEqual(S._classify_apdu('00b000000a'), 'read_binary')
+
+    def test_read_record(self):
+        self.assertEqual(S._classify_apdu('00b2010428'), 'read_record')
+
+    def test_other_not_classified(self):
+        self.assertIsNone(S._classify_apdu('80f2000c00'))
+
+    def test_short_input(self):
+        self.assertIsNone(S._classify_apdu(''))
+        self.assertIsNone(S._classify_apdu('00'))
+
+
+class TestApduTimeCollection(unittest.TestCase):
+    def setUp(self):
+        self.saved = (S._APDU_TIME_COLLECT, list(S._APDU_TIMES), S._server_ref)
+        S._APDU_TIME_COLLECT = False
+        S._APDU_TIMES.clear()
+        S._server_ref = None
+
+    def tearDown(self):
+        S._APDU_TIME_COLLECT, times, S._server_ref = self.saved
+        S._APDU_TIMES[:] = times
+
+    def test_disabled_does_not_collect(self):
+        tracer = S.StderrApduTracer()
+        with mock.patch.object(S.os, 'write'):
+            tracer.trace_command('00a40004023f0000')
+            tracer.trace_response('00a40004023f0000', '9000', '')
+        self.assertEqual(S._APDU_TIMES, [])
+
+    def test_collects_only_classified_commands_with_ms(self):
+        S._collect_apdu_times()
+        tracer = S.StderrApduTracer()
+        with mock.patch.object(S.os, 'write'):
+            tracer._cmd_start = time.time() - 0.025
+            tracer.trace_response('00a40004023f0000', '9000', '')
+            tracer._cmd_start = time.time() - 0.010
+            tracer.trace_response('00b000000a', '9000', '')
+            tracer._cmd_start = time.time() - 0.005
+            tracer.trace_response('80f2000c00', '9000', '')
+        times = S._end_apdu_time_collection()
+        self.assertEqual([t['type'] for t in times], ['select', 'read_binary'])
+        self.assertGreaterEqual(times[0]['ms'], 20)
+        self.assertFalse(S._APDU_TIME_COLLECT)
+        self.assertEqual(S._APDU_TIMES, [])
+
+    def test_collect_reattaches_tracer_when_missing(self):
+        tp = types.SimpleNamespace(apdu_tracer=None)
+        scc = types.SimpleNamespace(_tp=tp)
+        S._server_ref = types.SimpleNamespace(scc=scc)
+        S._collect_apdu_times()
+        try:
+            self.assertIsInstance(tp.apdu_tracer, S._LoggingApduTracer)
+        finally:
+            S._end_apdu_time_collection()
+
+    def test_collect_keeps_existing_tracer(self):
+        tracer = S.StderrApduTracer()
+        tp = types.SimpleNamespace(apdu_tracer=tracer)
+        scc = types.SimpleNamespace(_tp=tp)
+        S._server_ref = types.SimpleNamespace(scc=scc)
+        S._collect_apdu_times()
+        try:
+            self.assertIs(tp.apdu_tracer, tracer)
+        finally:
+            S._end_apdu_time_collection()
+
+
+if __name__ == '__main__':
+    unittest.main()