Misc. SM refactors + remove all warnings

[mirgee]

Add new initial state for issuer (to allow downloading proposal via update_state), use destructuring in connection SMs, rename inviter's / invitee'sNullState to InitialState, fix all compiler warnings for all features and tests, store thread id on SM level in connection SMs as well.

[codecov-commenter]

Codecov Report

Merging #374 (a595002) into main (845ed41) will decrease coverage by 19.55%.
The diff coverage is 54.73%.

@@             Coverage Diff             @@
##             main     #374       +/-   ##
===========================================
- Coverage   66.20%   46.65%   -19.56%     
===========================================
  Files         154      154               
  Lines       14593    13235     -1358     
  Branches     2873     2690      -183     
===========================================
- Hits         9662     6175     -3487     
- Misses       2602     5536     +2934     
+ Partials     2329     1524      -805     

Flag	Coverage Δ
integration-aries-vcx	?
unittests-agency-client	22.51% <ø> (ø)
unittests-aries-vcx	48.85% <54.73%> (+0.40%)	⬆️

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Impacted Files	Coverage Δ
agency_client/src/httpclient.rs	0.00% <ø> (ø)
...rc/handlers/connection/inviter/states/requested.rs	33.33% <0.00%> (ø)
aries_vcx/src/handlers/issuance/holder/holder.rs	42.30% <0.00%> (-16.73%)	⬇️
...vcx/src/handlers/issuance/issuer/states/initial.rs	0.00% <0.00%> (-68.97%)	⬇️
...ies_vcx/src/handlers/issuance/issuer/states/mod.rs	100.00% <ø> (ø)
aries_vcx/src/handlers/mod.rs	0.00% <0.00%> (-14.29%)	⬇️
...x/src/handlers/proof_presentation/prover/prover.rs	15.66% <ø> (-57.20%)	⬇️
...n/prover/states/presentation_preparation_failed.rs	60.00% <ø> (ø)
.../verifier/states/presentation_proposal_received.rs	87.50% <ø> (ø)
...c/handlers/proof_presentation/verifier/verifier.rs	34.48% <ø> (-29.32%)	⬇️
... and 111 more

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