Do not retry non-GET requests by default

[ichernev]

The main reason I started using this library is to do SSE events that require POST. As you can imagine, those have state and shouldn't be reset by the client without a good reason.

The default behavior (if no onerror and openWhenHidden) are specified is to reset on close and on tab switch... So this PR modifies the default behavior for non GET requests, to get some sane behavior out-of-the-box.

[ichernev]

@microsoft-github-policy-service agree company="DeepInfra"