Add docker-args flag to pass arguments to docker create command

This change allows users to pass additional arguments to the docker create command,
which can be useful for customizing the container environment (e.g. adding volumes,
setting resource limits, etc).

Co-Authored-By: sketch <hello@sketch.dev>

Update docker-args flag to handle space-separated arguments with escaping

- Created parseDockerArgs function to handle space-separated arguments with quotes and escaping
- Added comprehensive tests for argument parsing
- Updated CLI help text to reflect the new format

Co-Authored-By: sketch <hello@sketch.dev>
diff --git a/dockerimg/parse_args_test.go b/dockerimg/parse_args_test.go
new file mode 100644
index 0000000..7badcb7
--- /dev/null
+++ b/dockerimg/parse_args_test.go
@@ -0,0 +1,69 @@
+package dockerimg
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestParseDockerArgs(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected []string
+	}{
+		{
+			name:     "empty string",
+			input:    "",
+			expected: []string{},
+		},
+		{
+			name:     "single argument",
+			input:    "--memory=2g",
+			expected: []string{"--memory=2g"},
+		},
+		{
+			name:     "multiple arguments",
+			input:    "--memory=2g --cpus=2",
+			expected: []string{"--memory=2g", "--cpus=2"},
+		},
+		{
+			name:     "arguments with double quotes",
+			input:    "--label=\"my label\" --env=FOO=bar",
+			expected: []string{"--label=my label", "--env=FOO=bar"},
+		},
+		{
+			name:     "arguments with single quotes",
+			input:    "--label='my label' --env=FOO=bar",
+			expected: []string{"--label=my label", "--env=FOO=bar"},
+		},
+		{
+			name:     "nested quotes",
+			input:    "--env=\"KEY=\\\"quoted value\\\"\"",
+			expected: []string{"--env=KEY=\"quoted value\""},
+		},
+		{
+			name:     "mixed quotes",
+			input:    "--env=\"mixed 'quotes'\" --label='single \"quotes\"'",
+			expected: []string{"--env=mixed 'quotes'", "--label=single \"quotes\""},
+		},
+		{
+			name:     "escaped spaces",
+			input:    "--label=my\\ label --env=FOO=bar",
+			expected: []string{"--label=my label", "--env=FOO=bar"},
+		},
+		{
+			name:     "multiple spaces",
+			input:    "  --memory=2g   --cpus=2  ",
+			expected: []string{"--memory=2g", "--cpus=2"},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			result := parseDockerArgs(tc.input)
+			if !reflect.DeepEqual(result, tc.expected) {
+				t.Errorf("Expected %v, got %v", tc.expected, result)
+			}
+		})
+	}
+}