fix(rest): tolerate malformed x-ratelimit-reset in 429 handling

[MegaManSec]

Response.content() cast the x-ratelimit-reset header to int without validation. If a 429 response included a non-integer (or garbage) value, int() raised ValueError and the call crashed instead of raising a structured RateLimitError. Parse defensively and fall back to -1 when missing/malformed so clients always receive RateLimitError as intended.

Testing

Simulate a server response with something like this:

from auth0.exceptions import RateLimitError
from auth0.rest import Response

bad_headers = {"x-ratelimit-reset": "NaN"}  # or any non-integer
r = Response(429, {"error":"rate_limited"}, bad_headers)
r.content()  # raises ValueError today (expected: RateLimitError with reset_at=-1)

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors