feat: add -file-format flag for flexible output formats

Add support for -file-format flag to llgo build command allowing users to specify output format independently of target configuration.

Changes:
- Add -file-format flag supporting bin, hex, elf, uf2, zip formats
- Implement two-stage conversion: firmware format → file format
- Add ConvertOutput function with hex format conversion support
- Update build logic to handle different modes (build vs run/install)
- Add verbose logging for conversion operations

For build command: only convert firmware when -file-format is specified
For run/install commands: always convert firmware when target requires it

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

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

cmd/internal/flags/flags.go

@@ -8,9 +8,11 @@ import (
 )
 
 var OutputFile string
+var FileFormat string
 
 func AddOutputFlags(fs *flag.FlagSet) {
 	fs.StringVar(&OutputFile, "o", "", "Output file")
+	fs.StringVar(&FileFormat, "file-format", "", "File format for target output (e.g., bin, hex, elf, uf2, zip)")
 }
 
 var Verbose bool
@@ -48,6 +50,7 @@ func UpdateConfig(conf *build.Config) {
 	switch conf.Mode {
 	case build.ModeBuild:
 		conf.OutFile = OutputFile
+		conf.FileFormat = FileFormat
 	case build.ModeCmpTest:
 		conf.GenExpect = Gen
 	}