Move acquire/release to the connection vtable

[bretambrose]

The adapter's shutdown process needs to support additional logic within the scope of the state lock when the decision to shutdown is made (ref count zero). The simple ref count object in common cannot support this (atomic integers are insufficient), so we do the ref count by hand in the adapter so that we can disable the adapter inside the lock in one atomic action.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Patch coverage: 80.64% and no project coverage change.

Comparison is base (4885afb) 81.17% compared to head (bb1013d) 81.18%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #285   +/-   ##
=======================================
  Coverage   81.17%   81.18%           
=======================================
  Files          18       18           
  Lines        7311     7322   +11     
=======================================
+ Hits         5935     5944    +9     
- Misses       1376     1378    +2     

Impacted Files	Coverage Δ
source/mqtt3_to_mqtt5_adapter.c	76.19% <72.72%> (-2.19%)	⬇️
source/client.c	65.46% <100.00%> (+0.17%)	⬆️
source/client_impl_shared.c	77.27% <100.00%> (-0.51%)	⬇️

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