cache the frameHeaderBuffer & rentedArray

[bollhals]

Proposed Changes

This change adds a byte[6] cache to the SocketFrameHandler instead of stack allocating every time and then calling the Read extension method that then rented another byte[] which then copied the result to the stack allocated span.
=> Simplifies & improves performance.

We might reconsider the stack allocation again if we've moved to NS2.1 (I think this contains a Stream.Read(Span) function)

Also I extended the InboundFrame with the rented array, so one does not have to retrieve it again in the dispose.

Types of Changes

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

(The total execution duration is not relevant here, as it contains the waiting time for input in the socket. Look at the remaining functions. Before ~300ms, after ~200ms)
Performance before:

after:

[michaelklishin]

Good catch, thank you for your ongoing contributions @bollhals 💯