feat(cshared/,examples/c-app): Support compiling wallet SDK as a C library

[iurimatias]

For now just 2 APIs, to learn the paint points, see if it works etc..

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 77 lines in your changes missing coverage. Please review.
✅ Project coverage is 18.44%. Comparing base (63a2607) to head (fa57fc1).

Files with missing lines	Patch %	Lines
cshared/lib.go	0.00%	77 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           docs_specs      #13      +/-   ##
==============================================
- Coverage       19.64%   18.44%   -1.21%     
==============================================
  Files              17       18       +1     
  Lines            1181     1258      +77     
==============================================
  Hits              232      232              
- Misses            945     1022      +77     
  Partials            4        4              

Files with missing lines	Coverage Δ
cshared/lib.go	0.00% <0.00%> (ø)

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[dlipicar]

we probably want to "namespace" our function names a bit more, call this something like GoWSK_ethclient_NewClient

[saledjenic]

I didn't expect to have logic in this layer. Expected to have C bindings to expose wallet SDK functionality to a client. In that case, a client would take care of concurrency, storing ethcleints and so on.

for example:

func GoWSK_NewClient(rpcURL *C.char, errOut **C.char) C.uintptr_t {
	if rpcURL == nil {
		if errOut != nil {
			*errOut = C.CString("rpcURL is NULL")
		}
		return 0
	}
	url := C.GoString(rpcURL)
	rpcClient, err := gethrpc.Dial(url)
	if err != nil {
		if errOut != nil {
			*errOut = C.CString(err.Error())
		}
		return 0
	}
	client := sdkethclient.NewClient(rpcClient)
	h := cgo.NewHandle(client)
	return C.uintptr_t(h)
}

func GoWSK_ChainID(handle C.uintptr_t, errOut **C.char) *C.char {
	client := cgo.Handle(handle).Value().(*sdkethclient.Client)
	id, err := client.EthChainId(context.Background())
	if err != nil {
		if errOut != nil {
			*errOut = C.CString(err.Error())
		}
		return nil
	}
	return C.CString(id.String())
}