Remove generic UrsaError err mapping, handle possible UrsaErrors explicitly

[Patrik-Stas]

• Remove impl From<UrsaCryptoError> for AriesVcxError mapping - it seemed confusing, because it was not clear which of the error conditions can actually / in what circurmstance happen / where are ursa error thrown. In fact, most of the UrsaErrorKinds were never thrown. It turned out there's only 3 places where we deal with Ursa directly, and those errors are always about dealing with BigNumber conversions.
• So instead of the generic handling covering cases which don't happen, I've handled ursa errors directly on spot and converted them to new error kind UrsaError

Signed-off-by: Patrik Stas patrik.stas@absa.africa

[codecov-commenter]

Codecov Report

Merging #734 (0657ede) into main (4e4f02a) will decrease coverage by 24.32%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##             main     #734       +/-   ##
===========================================
- Coverage   54.00%   29.68%   -24.33%     
===========================================
  Files         371      368        -3     
  Lines       37656    31423     -6233     
  Branches     8184     6395     -1789     
===========================================
- Hits        20338     9327    -11011     
- Misses      11350    19343     +7993     
+ Partials     5968     2753     -3215     

Flag	Coverage Δ
unittests-aries-vcx	29.68% <0.00%> (-24.23%)	⬇️

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

Impacted Files	Coverage Δ
aries_vcx/src/errors/error.rs	40.54% <ø> (ø)
aries_vcx/src/plugins/anoncreds/credx_anoncreds.rs	10.30% <0.00%> (-53.79%)	⬇️
...tocols/proof_presentation/prover/states/initial.rs	0.00% <0.00%> (-100.00%)	⬇️
...cols/proof_presentation/verifier/states/initial.rs	0.00% <0.00%> (-100.00%)	⬇️
aries_vcx/src/handlers/discovery/mod.rs	0.00% <0.00%> (-93.94%)	⬇️
aries_vcx/tests/utils/scenarios.rs	0.00% <0.00%> (-80.47%)	⬇️
libvdrtools/src/domain/ledger/request.rs	0.00% <0.00%> (-79.49%)	⬇️
aries_vcx/src/utils/provision.rs	0.00% <0.00%> (-77.78%)	⬇️
...ies_vcx/src/core/profile/modular_wallet_profile.rs	0.00% <0.00%> (-76.48%)	⬇️
aries_vcx/src/plugins/anoncreds/indy_anoncreds.rs	2.70% <0.00%> (-75.68%)	⬇️
... and 207 more

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[gmulhearn]

lgtm!