test: improve pkg package coverage

- Add HTTP status error functions tests (internal/pkg/errors)
- Add ReadRequestBodyWithPrealloc tests (internal/pkg/httputil)
- Add HTTPStatusToGoogleStatus tests (internal/pkg/googleapi)

Coverage improvements:
- pkg/errors: 77.6%
- pkg/httputil: 91.7%
- pkg/googleapi: 79.5%

internal/pkg/httputil/body_test.go

@@ -0,0 +1,101 @@
+package httputil
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestReadRequestBodyWithPrealloc(t *testing.T) {
+	tests := []struct {
+		name          string
+		req           *http.Request
+		wantBody      []byte
+		wantErr       bool
+		wantNilResult bool
+	}{
+		{
+			name:          "nil_request",
+			req:           nil,
+			wantNilResult: true,
+		},
+		{
+			name: "nil_body",
+			req: &http.Request{
+				Body: nil,
+			},
+			wantNilResult: true,
+		},
+		{
+			name: "empty_body",
+			req: &http.Request{
+				Body:       http.NoBody,
+				ContentLength: 0,
+			},
+			wantBody: []byte{},
+		},
+		{
+			name: "small_body_content_length_100",
+			req: func() *http.Request {
+				body := strings.NewReader("small body content")
+				return &http.Request{
+					Body:          io.NopCloser(body),
+					ContentLength: 100,
+				}
+			}(),
+			wantBody: []byte("small body content"),
+		},
+		{
+			name: "large_body",
+			req: func() *http.Request {
+				data := bytes.Repeat([]byte("x"), 2000)
+				return &http.Request{
+					Body:          io.NopCloser(bytes.NewReader(data)),
+					ContentLength: 2000,
+				}
+			}(),
+			wantBody: bytes.Repeat([]byte("x"), 2000),
+		},
+		{
+			name: "very_large_body",
+			req: func() *http.Request {
+				data := bytes.Repeat([]byte("y"), 2<<20+1000) // > 2MB
+				return &http.Request{
+					Body:          io.NopCloser(bytes.NewReader(data)),
+					ContentLength: int64(2<<20 + 1000),
+				}
+			}(),
+			wantBody: bytes.Repeat([]byte("y"), 2<<20+1000),
+		},
+		{
+			name: "chunked_transfer_encoding",
+			req: func() *http.Request {
+				return &http.Request{
+					Body:          io.NopCloser(strings.NewReader("chunked data")),
+					ContentLength: -1,
+				}
+			}(),
+			wantBody: []byte("chunked data"),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ReadRequestBodyWithPrealloc(tt.req)
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			if tt.wantNilResult {
+				require.Nil(t, got)
+			} else {
+				require.Equal(t, tt.wantBody, got)
+			}
+		})
+	}
+}