Fix -template_params flag not being passed (Issue #149)

Resolves #149

The -template_params flag was defined in main.go but never passed to
the process.Options struct, making it non-functional. This was a bug
introduced in PR #90.

Changes:
- Added TemplateParams field to process.Options struct
- Updated main.go to pass *templateParams to process.Run()
- Updated process.go to parse JSON from TemplateParams string
- File-based params (-template_params_file) take precedence over
  string-based params (-template_params) if both are provided
- Added proper error handling for invalid JSON

The flag now works as intended:
  $ gotests -template_params '{"key":"value"}' -all file.go

Thanks to @butuzov for identifying this issue and @cweill for the fix suggestion!

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: cweill

gotests/main.go

@@ -101,6 +101,7 @@ func main() {
 		Template:           valOrGetenv(*template, "GOTESTS_TEMPLATE"),
 		TemplateDir:        valOrGetenv(*templateDir, "GOTESTS_TEMPLATE_DIR"),
 		TemplateParamsPath: *templateParamsPath,
+		TemplateParams:     *templateParams,
 		UseGoCmp:           *useGoCmp,
 	})
 }

gotests/process/process.go

@@ -35,6 +35,7 @@ type Options struct {
 	Template           string   // Name of custom template set
 	TemplateDir        string   // Path to custom template set
 	TemplateParamsPath string   // Path to custom parameters json file(s).
+	TemplateParams     string   // Custom parameters as JSON string
 	TemplateData       [][]byte // Data slice for templates
 	UseGoCmp           bool     // Use cmp.Equal (google/go-cmp) instead of reflect.DeepEqual
 }
@@ -76,6 +77,17 @@ func parseOptions(out io.Writer, opt *Options) *gotests.Options {
 	}
 
 	templateParams := map[string]interface{}{}
+
+	// Parse template params from JSON string if provided
+	if opt.TemplateParams != "" {
+		err := json.Unmarshal([]byte(opt.TemplateParams), &templateParams)
+		if err != nil {
+			fmt.Fprintf(out, "Failed to unmarshal template_params JSON: %s", err)
+			return nil
+		}
+	}
+
+	// Parse template params from file if provided (takes precedence)
 	jfile := opt.TemplateParamsPath
 	if jfile != "" {
 		buf, err := ioutil.ReadFile(jfile)