refactor: address review nits on material example

- name the example's stored size field blobSize, so it reads as the
  blob's size rather than the plaintext's
- keep chunkCountFor above encryptReader to cut diff churn

Assisted-by: Claude:claude-opus-5[1m]
Signed-off-by: Miroslav Bajtoš <oss@bajtos.net>

Author: bajtos

example_material_test.go

@@ -69,14 +69,14 @@ func ExampleDecryptRangeWithMaterial() {
 	// the blob's exact size.
 	row := struct {
 		material fee.BodyMaterial
-		size     int64
+		blobSize int64
 	}{material, int64(len(blob))}
 
 	// Serving a range later. Nothing here decodes the envelope — the reader is
 	// built from the stored row, so the only bytes fetched are ciphertext.
 	src := &countingBlob{blob: bytes.NewReader(blob), headerLen: row.material.HeaderLen}
 	const off, length = 4, 15
-	r, err := fee.DecryptRangeWithMaterial(src, row.size, row.material, cek, off, length)
+	r, err := fee.DecryptRangeWithMaterial(src, row.blobSize, row.material, cek, off, length)
 	if err != nil {
 		log.Fatal(err)
 	}

fee.go

@@ -408,6 +408,15 @@ func encryptStream(plaintext io.Reader, cek []byte, recipients []Recipient, opts
 	}, material, nil
 }
 
+// chunkCountFor reports how many STREAM chunks a plaintext of nPlain bytes
+// produces at the given chunk size. Empty input is one (empty) final chunk.
+func chunkCountFor(nPlain, chunkSize int64) int64 {
+	if nPlain <= 0 {
+		return 1
+	}
+	return (nPlain + chunkSize - 1) / chunkSize
+}
+
 // encryptReader is the wire blob [Encrypt] hands back: the encoded envelope
 // header, served from memory, followed by the ciphertext the background
 // encryption goroutine streams through the pipe.
@@ -423,15 +432,6 @@ func (e *encryptReader) Read(p []byte) (int, error) { return e.body.Read(p) }
 
 func (e *encryptReader) Close() error { return e.pr.Close() }
 
-// chunkCountFor reports how many STREAM chunks a plaintext of nPlain bytes
-// produces at the given chunk size. Empty input is one (empty) final chunk.
-func chunkCountFor(nPlain, chunkSize int64) int64 {
-	if nPlain <= 0 {
-		return 1
-	}
-	return (nPlain + chunkSize - 1) / chunkSize
-}
-
 // Decrypt recovers the plaintext from a FEE COSE_Encrypt (tag 96) envelope read
 // from src.
 //