Integration test refactoring

[mirgee]

• Splits test helper functions doing multiple distinct operations and returning many-valued tuples into small, reusable functions returning objects
• Moves ledger tests from aries_vcx/src/common/primitives/mod.rs and aries_vcx/src/common/primitives/revocation_registry_delta.rs to tests/test_pool.rs.
• Localizes test helper functions like create_indy_proof which ended up used in one test suite.
• Leaves only generic test helpers in aries_vcx/src/common/test_utils.rs.
• Issuance and presentation test helpers are strictly accepting concrete message types instead of generic AriesMessage (without implementing message-specific methods on issuance and presentation handlers, which can be done separately).

Although further test refactoring is warranted, the aim of this PR is to focus on integration tests (only those in aries_vcx/tests/).

[codecov-commenter]

Codecov Report

Merging #983 (8b8046a) into main (9b7ce90) will increase coverage by 0.39%.
The diff coverage is 89.33%.

❗ Current head 8b8046a differs from pull request most recent head fcda444. Consider uploading reports for the commit fcda444 to get more accurate results

@@            Coverage Diff             @@
##             main     #983      +/-   ##
==========================================
+ Coverage   28.89%   29.28%   +0.39%     
==========================================
  Files         419      417       -2     
  Lines       25981    26111     +130     
  Branches     5228     5223       -5     
==========================================
+ Hits         7506     7647     +141     
+ Misses      16271    16269       -2     
+ Partials     2204     2195       -9     

Flag	Coverage Δ
unittests-aries-vcx	29.28% <89.33%> (+0.39%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
aries_vcx/src/common/mod.rs	54.01% <ø> (ø)
...s_vcx/src/common/primitives/revocation_registry.rs	46.50% <0.00%> (ø)
...src/common/primitives/revocation_registry_delta.rs	26.66% <0.00%> (-26.07%)	⬇️
aries_vcx/src/handlers/issuance/holder.rs	42.13% <ø> (ø)
...es_vcx/tests/utils/scenarios/proof_presentation.rs	77.60% <45.45%> (+1.83%)	⬆️
...ies_vcx/src/common/primitives/credential_schema.rs	10.89% <50.00%> (+10.89%)	⬆️
...es_vcx/src/handlers/proof_presentation/verifier.rs	39.37% <75.00%> (ø)
aries_vcx/tests/test_pool.rs	85.60% <87.09%> (+0.98%)	⬆️
aries_vcx/src/common/credentials/mod.rs	81.66% <87.50%> (+5.90%)	⬆️
...s_vcx/tests/utils/scenarios/credential_issuance.rs	83.41% <89.18%> (+2.94%)	⬆️
... and 10 more

... and 5 files with indirect coverage changes