The Python (debugpy) and Go (delve-shim-dap) debug adapters unconditionally require network access on every debug session start — even when the adapter binary is already cached locally. This makes the debugger completely unusable offline.

Python: fetch_debugpy_whl → maybe_fetch_new_wheel hits pypi; failure propagates as a fatal error.
Go: install_shim → fetch_latest_adapter_version hits the GitHub API; failure propagates as a fatal error.
CodeLLDB and JavaScript adapters already handle this correctly.

Fix for Python and Go:

Wrap the network fetch in each adapter with a fallback: if the request fails and a previously downloaded adapter exists on disk, log a warning and use the cached version. If no cache exists, the original error propagates unchanged.

Logs after the fix:

2026-03-06T16:31:51+05:30 WARN  [dap_adapters::python] Failed to fetch latest debugpy, using cached version: getting latest release
2026-03-06T16:31:51+05:30 INFO  [dap::transport] Debug adapter has connected to TCP server 127.0.0.1:45533

Limitations:

The debugger must be run at least once with internet connectivity to populate the cache on disk. This PR does not change that requirement.

Closes #45781

Before you mark this PR as ready for review, make sure that you have:

• Added a solid test coverage and/or screenshots from doing manual testing
  • No automated tests are included. The existing MockDelegate stubs http_client() and fs() as unimplemented!(), so testing the fallback path would require new mock infrastructure. The fix was verified manually by running the debug build offline with and without cached adapters. The CodeLLDB adapter's equivalent fallback (lines 357-374) also has no dedicated test.
• Done a self-review taking into account security and performance aspects

Release Notes:

• Fixed debugger failing to start when offline if a debug adapter was previously downloaded.