Add custom types for type safety throughout codebase

- Add FileCount, FileSize, RelFilePath, AbsFilePath, ModTime, Multihash types
- Add UnixSeconds and UnixNanos types for timestamp handling
- Add URL types (ManifestURL, FileURL, BaseURL) with safe path joining
- Consolidate scanner package into mfer package
- Update checker to use custom types in Result and CheckStatus
- Add ModTime.Timestamp() method for protobuf conversion
- Update all tests to use proper custom types

internal/cli/gen.go

@@ -13,29 +13,29 @@ import (
 	"github.com/spf13/afero"
 	"github.com/urfave/cli/v2"
 	"sneak.berlin/go/mfer/internal/log"
-	"sneak.berlin/go/mfer/internal/scanner"
+	"sneak.berlin/go/mfer/mfer"
 )
 
 func (mfa *CLIApp) generateManifestOperation(ctx *cli.Context) error {
 	log.Debug("generateManifestOperation()")
 
-	opts := &scanner.Options{
+	opts := &mfer.ScannerOptions{
 		IncludeDotfiles: ctx.Bool("IncludeDotfiles"),
 		FollowSymLinks:  ctx.Bool("FollowSymLinks"),
 		Fs:              mfa.Fs,
 	}
 
-	s := scanner.NewWithOptions(opts)
+	s := mfer.NewScannerWithOptions(opts)
 
 	// Phase 1: Enumeration - collect paths and stat files
 	args := ctx.Args()
 	showProgress := ctx.Bool("progress")
 
 	// Set up enumeration progress reporting
-	var enumProgress chan scanner.EnumerateStatus
+	var enumProgress chan mfer.EnumerateStatus
 	var enumWg sync.WaitGroup
 	if showProgress {
-		enumProgress = make(chan scanner.EnumerateStatus, 1)
+		enumProgress = make(chan mfer.EnumerateStatus, 1)
 		enumWg.Add(1)
 		go func() {
 			defer enumWg.Done()
@@ -117,10 +117,10 @@ func (mfa *CLIApp) generateManifestOperation(ctx *cli.Context) error {
 	}()
 
 	// Phase 2: Scan - read file contents and generate manifest
-	var scanProgress chan scanner.ScanStatus
+	var scanProgress chan mfer.ScanStatus
 	var scanWg sync.WaitGroup
 	if showProgress {
-		scanProgress = make(chan scanner.ScanStatus, 1)
+		scanProgress = make(chan mfer.ScanStatus, 1)
 		scanWg.Add(1)
 		go func() {
 			defer scanWg.Done()