Fix RTM frame picker: use touch_start_time_rel/touch_end_time_rel to locate contact window instead of middle-of-video (which was pre-touch)

real_tactile_mnist/test-00000-of-00001.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:6c30d851fd9fd6b0bb6cbdea13f0500458c812caaad6e1955f99a5ac92b31676
-size 79466790
+oid sha256:1a02c8e9056923e6ba074f0d6a589a1607d627a18bb80b6e48d8fac76ad8b34a
+size 91191577

real_tactile_mnist/train-00000-of-00001.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:3e34860debbeab407b434692930a4f1a6f8f63c2aff9952b7bce8e82d6066ef2
-size 395763260
+oid sha256:1a9406cbe33d5dab97f9ac9413034d3f13198d459ee960d58a35bbb5430c8a02
+size 454827748