fix(retry): retry transient edge answers centrally, fix stale task test (#57)

- Route HTTP helpers (getJSON/formRequest/deleteReq/postJSON/putJSON/
  multipart upload), Query and AuthenticateContext/ensureToken through the
  deterministic 429/502/503/504 retry (retryRaw), so the integration suite
  no longer fails on the shared openresty rate limit under parallel runs.
- Fix stale cmd/office/fetch integration test: loader.TaskFields was
  replaced by loader.DetailForm (broke go vet -tags=integration).
- Add unit tests for Transient/DoRetry.

retry.go

@@ -2,6 +2,7 @@ package onlyoffice
 
 import (
 	"context"
+	"encoding/json"
 	"regexp"
 	"time"
 )
@@ -58,3 +59,16 @@ func DoRetry(ctx context.Context, p RetryPolicy, fn func() error) error {
 	}
 	return err
 }
+
+// retryRaw runs a transport attempt under the default transient-retry policy
+// and returns its raw payload. All HTTP helpers and Query() go through it, so
+// an openresty 429/502/503/504 is retried exactly like every bulk tool.
+func retryRaw(ctx context.Context, fn func() (json.RawMessage, error)) (json.RawMessage, error) {
+	var raw json.RawMessage
+	err := DoRetry(ctx, DefaultRetryPolicy(), func() error {
+		var e error
+		raw, e = fn()
+		return e
+	})
+	return raw, err
+}