feat(clients): idiomatic Go SDK client

[Salmatcre8]

Closes #145

What

Adds clients/go/ — a typed Go client for the Wraith API, mirroring the layout of the existing clients/python/. The module path is github.com/Miracle656/wraith/clients/go, so:

go get github.com/Miracle656/wraith/clients/go

Acceptance criteria

• ✅ One package per resource — transfers, accounts, assets, nfts, webhooks, status, each a standalone package, sharing a small transport in the root wraith package:

  Package	List methods
  transfers	Incoming, Outgoing, ForAddress, ByTx
  accounts	Summary, Transfers
  assets	PopularAssets
  nfts	Transfers
  webhooks	List, Deliveries
  status	Get
  wraith	shared Client/transport, APIError, options, query helpers

• ✅ Coverage tests — every package has httptest-based tests asserting request path/query shaping, response decoding, and *APIError mapping. go test ./... -cover passes (67–88% per package). The new .github/workflows/go-sdk.yml runs gofmt check, go vet, and go test ./... -race with a coverage summary.

Design notes

• wraith.New(baseURL, opts...) with WithHTTPClient / WithHeader; resource clients are constructed from it (transfers.New(c)).
• Amounts are returned as string to preserve full i128 precision (matching the Python client).
• Non-2xx responses are returned as *wraith.APIError (StatusCode, Message); usable with errors.As.
• Only the standard library is used (net/http, encoding/json, net/url).

Verification

• go build ./..., go vet ./..., gofmt -l . all clean.
• go test ./... -cover → all packages pass. (-race runs in CI on Linux; locally cgo/gcc isn't available, but the test handlers hold no cross-goroutine shared state.)

Note: the issue mentions the github.com/Miracle656/wraith-go import path; since the deliverable lives at clients/go/, the module is github.com/Miracle656/wraith/clients/go. A dedicated wraith-go repo or vanity import can alias it later if desired.

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[Miracle656]

Clean, fully-isolated Go SDK (clients/go/, own go.mod). Stdlib-only (net/http, encoding/json, net/url), one package per resource sharing a small transport, amounts as string to preserve i128 precision (matches the Python client), *wraith.APIError via errors.As. Every package has httptest-based tests for path/query shaping + decoding + error mapping — the dedicated 'Vet & test wraith-go' CI passes. The failing 'Typecheck & build' / 'Integration tests' are the Node jobs (pre-existing CI), unaffected by a Go-only PR. Closes #145.