normalizer: configurable float epsilon + JSON-path volatile mask scoping

Follow-ups to #4 normalizer PoC v2:
- Profile.float_decimals (default 6) flows into Rules.RoundFloatsInNode.
- mask_volatile_settings switches from name-only HashSet to a JSONPath-lite
  allowlist ($.a.b.c) so same-named fields in unrelated subtrees stay intact.
- default.yaml migrated; 6 new tests including a regression trap for the
  unrelated-subtree case. 16/16 normalizer tests, 77/77 solution tests.

Refs #2

src/Recordingtest.Normalizer/profiles/default.yaml

@@ -1,4 +1,5 @@
 name: default
+float_decimals: 6
 rules:
   - strip_timestamps
   - mask_guids
@@ -6,3 +7,20 @@ rules:
   - round_floats
   - mask_volatile_settings
   - sort_json_keys
+mask_volatile_settings:
+  - "$.CanOverrideWireColorWithFace"
+  - "$.IsSidePanelVisible"
+  - "$.OverrideFaceColor"
+  - "$.Solar_IsLocalTime"
+  - "$.VisibleGrid"
+  - "$.GridSnap"
+  - "$.MidpointOsnap"
+  - "$.GridSpacing"
+  - "$.GridColor.ALPHA"
+  - "$.GridColor.BLUE"
+  - "$.GridColor.GREEN"
+  - "$.GridColor.RED"
+  - "$.MajorGridColor.ALPHA"
+  - "$.MajorGridColor.BLUE"
+  - "$.MajorGridColor.GREEN"
+  - "$.MajorGridColor.RED"