Fix flush() to retry fetch() on transient errors

[penberg]

This changes flush() to retry the fetch() call on transient errors such as EPIPE, ECONNREFUSED, and ECONNRESET.

[mateusfreira]

Will that really solve the issue?
Don't you need to in the catch of the promise here

hrana-client-ts/src/http/stream.ts

Line 350 in 5d5bcdf

this._setClosed(error);

?

Unless fetch throws that error synchronously (I kinda doubt it does), I think it will escape your solution.

[penberg]

@mateusfreira I think that point is too late to safely retry because it covers things like failing to process the response. For example, we may have successfully executed a INSERT statement and committed it to the database, but fail later on. Retrying would mean a duplicate insert.

[penberg]

@mateusfreira I did switch to catching errors from the promise returned by fetch(), though, and added exponential backoff.