Replace Babel with SWC for test transpilation

Babel was only used via @babel/register to transform ESM imports and JSX
at runtime for ava tests. SWC does the same job significantly faster with
fewer dependencies (net removal of 60 packages).

- Delete .babelrc, replace with .swcrc
- Delete .nycrc (only referenced Babel-specific istanbul config, unused by c8)
- Swap @babel/* deps for @swc/core + @swc-node/register
- Update ava config to use @swc-node/register with SWCRC=true

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: KidkArolis

.babelrc

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "no-unused-vars": "off"
+  }
+}

.nycrc

@@ -0,0 +1,16 @@
+{
+  "jsc": {
+    "parser": {
+      "syntax": "ecmascript",
+      "jsx": true
+    },
+    "transform": {
+      "react": {
+        "runtime": "classic"
+      }
+    }
+  },
+  "module": {
+    "type": "commonjs"
+  }
+}

.oxlintrc.json

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+- Replace Babel with SWC for test transpilation, reducing dev dependencies significantly.
+
 ## 0.4.7
 
 - Fix the release, publish the right directory.