chore: move converter methods users v2 to separate converter package + add tests (#10567)

# Which Problems Are Solved

As requested by @adlerhurst in
https://github.com/zitadel/zitadel/pull/10415#discussion_r2298087711 , I
am moving the refactoring of v2 user converter methods to a separate PR

# How the Problems Are Solved

Cherry-pick 648c234caf

# Additional Context

Parent of https://github.com/zitadel/zitadel/pull/10415

(cherry picked from commit b604615cab)

internal/api/grpc/user/v2/convert/machine_test.go

@@ -0,0 +1,108 @@
+package convert
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/zitadel/zitadel/internal/domain"
+	"github.com/zitadel/zitadel/internal/query"
+	"github.com/zitadel/zitadel/pkg/grpc/user/v2"
+)
+
+func Test_accessTokenTypeToPb(t *testing.T) {
+	t.Parallel()
+	tt := []struct {
+		name     string
+		input    domain.OIDCTokenType
+		expected user.AccessTokenType
+	}{
+		{
+			name:     "Bearer token type",
+			input:    domain.OIDCTokenTypeBearer,
+			expected: user.AccessTokenType_ACCESS_TOKEN_TYPE_BEARER,
+		},
+		{
+			name:     "JWT token type",
+			input:    domain.OIDCTokenTypeJWT,
+			expected: user.AccessTokenType_ACCESS_TOKEN_TYPE_JWT,
+		},
+		{
+			name:     "Unknown token type returns Bearer",
+			input:    domain.OIDCTokenType(2),
+			expected: user.AccessTokenType_ACCESS_TOKEN_TYPE_BEARER,
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := accessTokenTypeToPb(tc.input)
+			require.Equal(t, tc.expected, got)
+		})
+	}
+}
+
+func Test_machineToPb(t *testing.T) {
+	t.Parallel()
+
+	tt := []struct {
+		name     string
+		input    *query.Machine
+		expected *user.MachineUser
+	}{
+		{
+			name: "All fields set, Bearer token, HasSecret true",
+			input: &query.Machine{
+				Name:            "machine1",
+				Description:     "desc",
+				EncodedSecret:   "secret",
+				AccessTokenType: domain.OIDCTokenTypeBearer,
+			},
+			expected: &user.MachineUser{
+				Name:            "machine1",
+				Description:     "desc",
+				HasSecret:       true,
+				AccessTokenType: user.AccessTokenType_ACCESS_TOKEN_TYPE_BEARER,
+			},
+		},
+		{
+			name: "No secret, JWT token",
+			input: &query.Machine{
+				Name:            "machine2",
+				Description:     "desc2",
+				EncodedSecret:   "",
+				AccessTokenType: domain.OIDCTokenTypeJWT,
+			},
+			expected: &user.MachineUser{
+				Name:            "machine2",
+				Description:     "desc2",
+				HasSecret:       false,
+				AccessTokenType: user.AccessTokenType_ACCESS_TOKEN_TYPE_JWT,
+			},
+		},
+		{
+			name: "Unknown token type, HasSecret false",
+			input: &query.Machine{
+				Name:            "machine3",
+				Description:     "desc3",
+				EncodedSecret:   "",
+				AccessTokenType: domain.OIDCTokenType(99),
+			},
+			expected: &user.MachineUser{
+				Name:            "machine3",
+				Description:     "desc3",
+				HasSecret:       false,
+				AccessTokenType: user.AccessTokenType_ACCESS_TOKEN_TYPE_BEARER,
+			},
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := machineToPb(tc.input)
+			require.Equal(t, tc.expected, got)
+		})
+	}
+}