feat(near-sdk): use #[serde_as] for #[near(serializers = [json])]

[mitinarseny]

This PR lets contracts to use serde_with crate by automatically adding #[serde_as] attribute when json serializer is enabled in #[near] macro.

serde_with leverages Rust type system and lets to avoid introducing newtypes (such as U128) to just redefine how to serialize/deserialize the underlying type. Newtype approach is very cumbersome and inconvenient to work with, especially when dealing with nested collections.

Right now smart-contract devs are forced to use some dirty hacks in order to achieve it, as well as introduce fake features that are required for cargo near build to work due to manual features activation via cli for near-sdk.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.61%. Comparing base (5cc4fcf) to head (61322a8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1393      +/-   ##
==========================================
- Coverage   80.87%   80.61%   -0.26%     
==========================================
  Files         104      104              
  Lines       15464    15470       +6     
==========================================
- Hits        12506    12471      -35     
- Misses       2958     2999      +41     

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[frol]

/compare

[github-actions]

Contract size report

Sizes are given in bytes.

contract	master	this branch	difference
adder.wasm	66347	66347	+0%
approval_receiver.wasm	83957	84097	+0%
callback_results.wasm	80667	80667	+0%
cross_contract_high_level.wasm	71618	71618	+0%
cross_contract_low_level.wasm	67378	67378	+0%
defi.wasm	87540	87691	+0%
factory_contract_high_level.wasm	161720	161712	-0%
factory_contract_low_level.wasm	157182	157174	-0%
fungible_token.wasm	143922	144026	+0%
lockable_fungible_token.wasm	107021	107024	+0%
mission_control.wasm	108324	108324	+0%
mpc_contract.wasm	101052	101052	+0%
non_fungible_token.wasm	198488	198436	-0%
status_message.wasm	81766	81758	-0%
test_contract.wasm	20490	20490	+0%
token_receiver.wasm	83773	83894	+0%
versioned.wasm	89567	89567	+0%

[PolyProgrammist]

Hi! Could you please add a test that shows the benefit from the feature

[mitinarseny]

@PolyProgrammist Sure! I've added to #[near] macro docs along with doctests

[PolyProgrammist]

Looks good to me. @frol do you have anything to add?