crypto/sha256: make digest sum public (#10047)

vlib/crypto/sha256/sha256.v

@@ -124,7 +124,7 @@ fn (mut d Digest) write(p_ []byte) ?int {
 	}
 }
 
-fn (d &Digest) sum(b_in []byte) []byte {
+pub fn (d &Digest) sum(b_in []byte) []byte {
 	// Make a copy of d so that caller can keep writing and summing.
 	mut d0 := *d
 	hash := d0.checksum()

vlib/crypto/sha256/sha256_test.v

@@ -8,3 +8,12 @@ fn test_crypto_sha256() {
 	assert sha256.sum('This is a sha256 checksum.'.bytes()).hex() ==
 		'dc7163299659529eae29683eb1ffec50d6c8fc7275ecb10c145fde0e125b8727'
 }
+
+fn test_crypto_sha256_writer() {
+	mut digest := sha256.new()
+	digest.write('This is a'.bytes()) or { assert false }
+	digest.write(' sha256 checksum.'.bytes()) or { assert false }
+	sum := digest.sum([])
+	assert sum.hex() ==
+		'dc7163299659529eae29683eb1ffec50d6c8fc7275ecb10c145fde0e125b8727'
+}