Let a variant's methods nest under its components

A multi-component variant could only declare one flat methods map, so a
pipeline whose parts share a method name had nowhere to put them: supertonic
has four forwards, kokoro two. A methods value may now be either a signature
or a map of signatures keyed by method name, selected by component.

Purely additive: every config that validated before still validates.

config.schema.json

@@ -112,7 +112,13 @@
         "methods": {
           "type": "object",
           "minProperties": 1,
-          "additionalProperties": { "$ref": "#/$defs/methodSignature" }
+          "additionalProperties": {
+            "oneOf": [
+              { "$ref": "#/$defs/methodSignature" },
+              { "$ref": "#/$defs/componentMethods" }
+            ]
+          },
+          "description": "Single-file variants key this by method name. Multi-component variants key it by component name, matching `components`, and nest that component's methods inside."
         }
       },
       "oneOf": [
@@ -138,6 +144,12 @@
         }
       }
     },
+    "componentMethods": {
+      "type": "object",
+      "minProperties": 1,
+      "additionalProperties": { "$ref": "#/$defs/methodSignature" },
+      "description": "One component's methods, keyed by method name. Used under `methods` when a variant sets `components`, so that components sharing a method name (several `forward`s in one pipeline) stay distinct."
+    },
     "tensorSpec": {
       "type": "object",
       "required": ["shape", "dtype"],