Resolve DEP0169 url.parse() deprecation and add ESM support

[alexmyshchyshyn]

• Removed unused @open-rpc/client-js dependency

  • Its compiled mock invoked url.parse(), triggering DEP0169 warnings during test runs

• Switched Axios to the built-in fetch adapter (adapter: 'fetch')

  • Bypasses follow-redirects, which was calling url.parse() on every RPC request

• Fixed HttpError being swallowed in processFetchRequest

  • Moved the status check outside the try/catch so errors propagate correctly to callers

• Added Webpack ESM build target (lib.esm.js)

  • Uses experiments.outputModule

• Updated package.json

  • Added "exports" and "module" fields for proper ESM/CJS resolution
  • Fixes named imports in modern TypeScript projects

• Added "engines": { "node": ">=18" }

  • Reflects the requirement for the fetch adapter

• Added unit tests for HttpHandler

  • Covers both Axios and fetch client paths

• Resolves: Node.js v22 Deprecation: url.parse() via @open-rpc/client-js #595

• Resolves: Imports not working in modern TypeScript project #567

[davidatwhiletrue]

LGTM