Jstz proto: fix kv value serialization

[ryutamago]

Context

Bug:
Running the example/counter.js sf fails on the second time, resulitng in derserialization error (Serde(AnyNotSupported))

Cause:
KvValue currently relies on #[bincode(with_serde)] for deserializing the serde_json::Value. This forcese bincode to invokes serde_json's deserialize method. For example, in serde_json, the Number type is deserialized using deserialized_any method.

However the deserializer, provided by bincode decoder, doesn't support deserializing "any" type, resulting in an error.

This PR fix this issue by manually implementing Decode/Encode method.

Task link

Description

• implement Decode/Encode manually on KvValue
• Removed the old (de)serialization method to string as it's not used anymore

Manually testing the PR

add unit tests for KvValue

cargo test --package jstz_proto --lib -- api::kv::tests --show-output 

manually tested by deploying sf counter.js and runnig it twice.

Before:

─(12:32:36 on leounoki-jstz-285/fix-kv-value ✹)──> cargo run --bin jstz run tezos://tz1Lpp7y6gsXzPgoU6dd26uM1hrc5x2qprGB/ --network dev --trace
    
Connected to trace smart function "tz1Lpp7y6gsXzPgoU6dd26uM1hrc5x2qprGB"
[🪵]: Counter: null
Status code: 200 OK
Headers: {}
┌─(~/tezos/jstz)───────────────────────────(leo@Leos-MacBook-Pro:s007)─┐
└─(12:32:47 on leounoki-jstz-285/fix-kv-value ✹)──> cargo run --bin jstz run tezos://tz1Lpp7y6gsXzPgoU6dd26uM1hrc5x2qprGB/ --network dev --trace
// fails with `AnyNotSupported` as `Number` cannot be deserialized by bincode

After:

─(12:32:36 on leounoki-jstz-285/fix-kv-value ✹)──> cargo run --bin jstz run tezos://tz1Lpp7y6gsXzPgoU6dd26uM1hrc5x2qprGB/ --network dev --trace
    
Connected to trace smart function "tz1Lpp7y6gsXzPgoU6dd26uM1hrc5x2qprGB"
[🪵]: Counter: null
Status code: 200 OK
Headers: {}
┌─(~/tezos/jstz)───────────────────────────(leo@Leos-MacBook-Pro:s007)─┐
└─(12:32:47 on leounoki-jstz-285/fix-kv-value ✹)──> cargo run --bin jstz run tezos://tz1Lpp7y6gsXzPgoU6dd26uM1hrc5x2qprGB/ --network dev --trace

Connected to trace smart function "tz1Lpp7y6gsXzPgoU6dd26uM1hrc5x2qprGB"
[🪵]: Counter: 0
Status code: 200 OK
Headers: {}

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 8 lines in your changes missing coverage. Please review.

Project coverage is 49.33%. Comparing base (6e56c16) to head (7b7ca97).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/jstz_proto/src/api/kv.rs	86.66%	3 Missing and 5 partials ⚠️

Files with missing lines	Coverage Δ
crates/jstz_proto/src/api/kv.rs	50.00% <86.66%> (+27.31%)	⬆️

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6e56c16...7b7ca97. Read the comment docs.

[zcabter]

Thanks for the fix