Fix read_bytes31 (#340)

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## Pull Request type

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Please check the type of change your PR introduces:

- [x] Bugfix
- [ ] Feature
- [ ] Code style update (formatting, renaming)
- [ ] Refactoring (no functional changes, no API changes)
- [ ] Build-related changes
- [ ] Documentation content changes
- [ ] Other (please describe):

## What is the current behavior?

read_bytes31 does not begin at the offset. This is incorrect standalone
behavior and creates an infinite loop in the .into() function (from
ByteTrait to ByteArray) if there is more than 61 bytes in the bytes
struct

Issue Number: N/A

## What is the new behavior?

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this PR. -->

Starts at the right offset

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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impact and migration path for existing applications below. -->

## Other information

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packages/bytes/src/bytes.cairo

@@ -393,7 +393,7 @@ impl BytesImpl of BytesTrait {
     #[inline(always)]
     fn read_bytes31(self: @Bytes, offset: usize) -> (usize, bytes31) {
         // Read 31 bytes of data ( 16 bytes high + 15 bytes low )
-        let (new_offset, high) = self.read_u128(0);
+        let (new_offset, high) = self.read_u128(offset);
         let (new_offset, low) = self.read_u128_packed(new_offset, 15);
         // low bits shifting to remove the left padded 0 byte on u128 type
         let low = U128BitShift::shl(low, 8);

packages/bytes/src/tests/test_bytes.cairo

@@ -355,11 +355,11 @@ fn test_bytes_read_u256() {
 #[available_gas(20000000)]
 fn test_bytes_read_bytes31() {
     let bytes: Bytes = BytesTrait::new(
-        31, array![0x0102030405060708090a0b0c0d0e0f10, 0x1112131415161718191a1b1c1d1e1f00]
+        42, array![0x0102030405060708090a0b0c0d0e0f10, 0x1112131415161718191a1b1c1d1e1f17, 0x0]
     );
-    let (offset, val) = bytes.read_bytes31(0);
-    assert_eq!(offset, 31);
-    let byte31: bytes31 = 0x0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f
+    let (offset, val) = bytes.read_bytes31(2);
+    assert_eq!(offset, 33);
+    let byte31: bytes31 = 0x030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f1700
         .try_into()
         .unwrap();
     assert!(val == byte31, "read_bytes31 test failed")
@@ -688,7 +688,7 @@ fn test_bytes_sha256() {
 #[test]
 fn test_byte_array_conversions() {
     let bytes = BytesTrait::new(
-        52,
+        64,
         array![
             0x01020304050607080910111213141516,
             0x16151413121110090807060504030201,