simplify ack/nack handling

[bollhals]

Proposed Changes

There are three main changes here:

• Cleans up some unused methods in AutorecoveringModel / ExtensionMethods
• Avoids allocating a BasicAckEventArgs / BasicNackEventArgs if there is no handler.
• Changes HandleAckNack to call _deliveryTagsCountdown.Signal(count); instead of repeatedly _deliveryTagsCountdown.Signal()

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

Allocations before:

After:

Performance before: (consider both methods as it got inlined HandleBasicAck & handleAckNack)

after: