types/model: remove Digest

The Digest type in its current form is awkward to work with and presents
challenges with regard to how it serializes via String using the '-'
prefix.

We currently only use this in ollama.com, so we'll move our specific
needs around digest parsing and validation there.

types/model/name.go

@@ -4,7 +4,6 @@ package model
 
 import (
 	"cmp"
-	"encoding/hex"
 	"errors"
 	"fmt"
 	"log/slog"
@@ -371,57 +370,3 @@ func cutPromised(s, sep string) (before, after string, ok bool) {
 	}
 	return cmp.Or(before, MissingPart), cmp.Or(after, MissingPart), true
 }
-
-type DigestType byte
-
-const (
-	DigestTypeInvalid DigestType = iota
-	DigestTypeSHA256
-)
-
-func (t DigestType) String() string {
-	switch t {
-	case DigestTypeSHA256:
-		return "sha256"
-	default:
-		return "invalid"
-	}
-}
-
-type Digest struct {
-	Type DigestType
-	Sum  [32]byte
-}
-
-func ParseDigest(s string) (Digest, error) {
-	i := strings.IndexAny(s, "-:")
-	if i < 0 {
-		return Digest{}, fmt.Errorf("invalid digest %q", s)
-	}
-	typ, encSum := s[:i], s[i+1:]
-	if typ != "sha256" {
-		return Digest{}, fmt.Errorf("unsupported digest type %q", typ)
-	}
-	d := Digest{
-		Type: DigestTypeSHA256,
-	}
-	n, err := hex.Decode(d.Sum[:], []byte(encSum))
-	if err != nil {
-		return Digest{}, err
-	}
-	if n != 32 {
-		return Digest{}, fmt.Errorf("digest %q decoded to %d bytes; want 32", encSum, n)
-	}
-	return d, nil
-}
-
-func (d Digest) String() string {
-	if d.Type == DigestTypeInvalid {
-		return ""
-	}
-	return fmt.Sprintf("sha256-%x", d.Sum)
-}
-
-func (d Digest) IsValid() bool {
-	return d.Type != DigestTypeInvalid
-}