fix(state): JSON marshaling for sdk Address wrapper

[distractedm1nd]

While debugging #2322 , I noticed that it is not only an RPC issue, but also a broken API one. All RPC methods that used the type state.Address were unusable, both via the client and via raw JSON calls. This is because the server was unable to marshal the address string value back into the interface type.

To circumvent this, I have embedded the sdk.Address type in the same way that we embed the fraud proof type, to allow us to unmarshal it back into a concrete type. I have also added unit tests to fix this.

In addition, it fixes the RPC parsing - so it closes #2322 .

[Wondertan]

So the core issue here is that cosmos sdk addresses does not implement json serialisation and reflection does not work automatically, right?

[Wondertan]

Thanks the tests!

[codecov-commenter]

Codecov Report

Merging #2348 (41b1fe4) into main (c41738a) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #2348      +/-   ##
==========================================
- Coverage   50.84%   50.82%   -0.02%     
==========================================
  Files         154      155       +1     
  Lines        9746     9760      +14     
==========================================
+ Hits         4955     4961       +6     
- Misses       4355     4365      +10     
+ Partials      436      434       -2     

Impacted Files	Coverage Δ
api/gateway/state.go	7.85% <0.00%> (ø)
cmd/celestia/rpc.go	10.00% <0.00%> (+0.11%)	⬆️
state/core_access.go	27.14% <0.00%> (ø)
state/state.go	0.00% <0.00%> (ø)

... and 4 files with indirect coverage changes