[feature] #2645: Unions in FFI

[mversic]

Signed-off-by: Marin Veršić [email protected]

Description of the Change

• introduce a handy ffi_type! function like macro to declare your type
• disable the use of mutable non robust references by default
• attach ffi_type prefix to FfiType helper macro attributes
• add repr(transparent) where applicable
• improve serialization of transparent structures (introduce ffi_type(unsafe {robust}) or derive the Transmute trait manually)
• implement serialization for unions
• implement serialization of ConstString (out-pointers are still TBD)
• fix NonLocal impls

Issue

Closes #2645 #2669 #2800 #2790 #2796

Benefits

Possible Drawbacks

Usage Examples or Tests [optional]

Alternate Designs [optional]

[codecov]

Codecov Report

Merging #2837 (f1bb7e0) into iroha2-dev (a16d9c3) will decrease coverage by 4.88%.
The diff coverage is 75.89%.

@@              Coverage Diff               @@
##           iroha2-dev    #2837      +/-   ##
==============================================
- Coverage       67.61%   62.72%   -4.89%     
==============================================
  Files             140      168      +28     
  Lines           26173    29576    +3403     
==============================================
+ Hits            17696    18552     +856     
- Misses           8477    11024    +2547     

Impacted Files	Coverage Δ
actor/src/actor_id.rs	90.00% <ø> (ø)
actor/src/deadlock.rs	85.93% <ø> (-14.07%)	⬇️
cli/derive/src/lib.rs	92.30% <ø> (+17.58%)	⬆️
cli/src/event.rs	0.00% <ø> (-41.87%)	⬇️
cli/src/main.rs	1.09% <0.00%> (-0.26%)	⬇️
cli/src/stream.rs	0.00% <ø> (-81.40%)	⬇️
client/src/http.rs	47.82% <ø> (ø)
client/src/http_default.rs	40.17% <0.00%> (-20.01%)	⬇️
client_cli/src/main.rs	0.27% <0.00%> (+0.01%)	⬆️
config/base/src/runtime_upgrades.rs	49.42% <0.00%> (ø)
... and 231 more

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