fix: remove custom proxy handling (#143)

Undici has added native support for proxy handling, so it is no longer necessary for us to have our own custom proxy handling.

Reverts #102 and resolves #134.

package-lock.json

@@ -12,8 +12,7 @@
         "@actions/core": "^1.11.1",
         "@octokit/auth-app": "^7.2.1",
         "@octokit/request": "^9.2.2",
-        "p-retry": "^6.2.1",
-        "undici": "^7.8.0"
+        "p-retry": "^6.2.1"
       },
       "devDependencies": {
         "@octokit/openapi": "^19.1.0",
@@ -24,6 +23,7 @@
         "esbuild": "^0.25.8",
         "execa": "^9.6.0",
         "open-cli": "^8.0.0",
+        "undici": "^7.13.0",
         "yaml": "^2.8.1"
       },
       "engines": {
@@ -3817,6 +3817,7 @@
       "version": "7.13.0",
       "resolved": "https://registry.npmjs.org/undici/-/undici-7.13.0.tgz",
       "integrity": "sha512-l+zSMssRqrzDcb3fjMkjjLGmuiiK2pMIcV++mJaAc9vhjSGpvM7h43QgP+OAMb1GImHmbPyG2tBXeuyG5iY4gA==",
+      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">=20.18.1"