Reduce the memory footprint of ManagedWebSocket

[zlatanov]

While working on the websocket compression I noticed two things but decided to leave them after the feature was completed:

1. There was a static readonly instance of RandomNumberGenerator, which could be replaced with RandomNumberGenerator.Fill.
2. The ManagedWebSocket class was creating CancellationTokenSource but never really used the cancellation part. Since continuations from CancellationTokenSource.Cancel are executed synchronously, the cancellation source could be replaced with a method.

This reduced the memory footprint of a websocket without compression enabled from 752 bytes to 552 bytes.

//cc @CarnaViire @scalablecory

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Issue Details

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While working on the websocket compression I noticed two things but decided to leave them after the feature was completed:

1. There was a static readonly instance of RandomNumberGenerator, which could be replaced with RandomNumberGenerator.Fill.
2. The ManagedWebSocket class was creating CancellationTokenSource but never really used the cancellation part. Since continuations from CancellationTokenSource.Cancel are executed synchronously, the cancellation source could be replaced with a method.

This reduced the memory footprint of a websocket without compression state from 752 bytes to 552 bytes.

//cc @CarnaViire @scalablecory

Author:	zlatanov
Assignees:	-
Labels:	area-System.Net
Milestone:	-

[MihaZupan]

LGTM, I see no reason why we'd want to use a CTS here

[CarnaViire]

FYI: CI failures are ongoing infra issue. I will rerun checks after it's fixed

[zlatanov]

@CarnaViire the failing tests seem unrelated. Let me know if anything else is needed.

[CarnaViire]

@zlatanov sorry for delaying on the rerun 😔 I've triggered it now
As I understood it, because of the CI issue on Thursday-Friday, it didn't run the whole Browser wasm testing step, so I believe it's better to wait for it to complete. Hopefully it'll be green so I'll merge it afterwards 🙂