fix(fetch): forward endpoint, isImport, and body unchanged on retry

[walm]

Fixes #17.

The retry after a 5xx in makeRequest rebuilt the named arguments and got three of them wrong:

• endpoint was not passed, so the retried request went to the bare node URL with no path and got a 404.
• isImport was not passed and reset to false, so a retried import lost its text/plain content type and its JSONL body was JSON.stringified.
• body was pre-stringified for non-import requests, then stringified again at the fetch call, so the server received a double-encoded string.

This forwards all arguments unchanged. The fetch call already handles the import/non-import body distinction.

Added two regression tests to tests/fetch/request.test.ts in the style of the existing ones. Both fail against the current 1.0.0 branch and pass with the fix:

• retry after a 5xx keeps the endpoint path and sends an identical body
• retry of an import keeps the JSONL body and text/plain content type

Ran vitest run tests/fetch/request.test.ts (8 passed), tsc --noEmit, eslint, and prettier --check on the changed files.