fix(genapi): scope method-param enums per method, dedupe case-colliding enum consts

Bot API update added RichBlockListItem.type values (a/A/i/I/1) that
Pascal-case to identical const idents, and answerGuestQuery's non-enum
'result' param picked up answerChatJoinRequestQuery's Result enum via
the shared parent="" enum-plan key.

- key method params as method:<name> in the enum plan byField map
- enumDecl.ConstName resolves case collisions with Lower/Upper prefix
- regenerate api/ from 2026-06-11 snapshot

cmd/genapi/extra_test.go

@@ -574,7 +574,7 @@ func TestSentinelForField(t *testing.T) {
 	}
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {
-			got := sentinelForField(c.field, unionTypes, nil)
+			got := sentinelForField("testMethod", c.field, unionTypes, nil)
 			require.Contains(t, got, c.contains, "sentinelForField for %q", c.name)
 		})
 	}