fix(sio-client): reset the flags once a packet is queued

[giaBaoJS]

The kind of change this PR does introduce

• a bug fix
• a new feature
• an update to the documentation
• a code change that improves performance
• other

Current behavior

With the retries option, emit() hands the packet to _addToQueue(), which copies this.flags into the queued packet but never clears them. emit() then returns early, so the usual this.flags = {} at the end is skipped. The flags are only reset when _drainQueue() happens to send something right away, which does not happen when the socket is not connected yet or when an earlier packet is still waiting for its ack.

In that case a one-shot modifier like compress(false) or timeout() sticks to every following emit:

const socket = io({ autoConnect: false, retries: 3, ackTimeout: 10000 });

socket.timeout(100).emit("a", () => {});
socket.emit("b", () => {});
socket.emit("c", () => {});

// queued flags:
// a: { fromQueue: true, timeout: 100 }
// b: { fromQueue: true, timeout: 100 }   <- should use ackTimeout
// c: { fromQueue: true, timeout: 100 }

Same thing once connected, if socket.compress(false).emit("x") is called while another packet is pending: the next emit() is sent uncompressed too.

New behavior

The flags are cleared once they have been copied into the queued packet, so they only apply to that packet (including its retries), like they do without retries.

Other information (e.g. related issues)

I could not find an existing issue for this.

Two tests added to test/retry.ts, one for the "not connected yet" case and one for the "previous packet pending" case. They check the compress option of each packet on packetCreate. Without the change they fail with expected [ false, false ] to sort of equal [ false, true ] and expected [ true, false, false ] to sort of equal [ true, false, true ]. npm test --workspace=socket.io-client passes (114 tests).