test: improve coverage for builtin/bytes.mbt

**Disclaimer:** This PR was generated by an LLM agent as part of an experiment.

## Summary

```
coverage of `builtin/bytes.mbt`: 78.6% -> 100%
```

Author: rami3l

builtin/bytes_test.mbt

@@ -166,3 +166,57 @@ test "fixedarray_byte_blit_from_bytes" {
   arr.blit_from_bytes(0, bytes, 0, bytes.length())
   inspect!(arr, content="[b'\\x48', b'\\x65', b'\\x6C', b'\\x6C', b'\\x6F']")
 }
+
+///|
+test "Bytes::op_equal with differing bytes" {
+  let bytes1 = b"\x01\x02\x03"
+  let bytes2 = b"\x01\x02\xFF" // Same length as bytes1 but last byte differs
+  inspect!(bytes1 == bytes2, content="false")
+}
+
+///|
+test "blit_from_bytesview basic case" {
+  let arr = FixedArray::make(4, b'\x00')
+  let view = b"\x01\x02\x03"[1:] // view contains "\x02\x03"
+  arr.blit_from_bytesview(1, view)
+  inspect!(arr, content="[b'\\x00', b'\\x02', b'\\x03', b'\\x00']")
+}
+
+///|
+test "panic FixedArray::set_utf8_char/invalid_code_point" {
+  let buf = FixedArray::make(4, b'\x00')
+  // Creating a character with code point greater than 0x10FFFF (1114111)
+  let invalid_char = Char::from_int(0x110001)
+  // This should trigger the "Char out of range" panic
+  let _ = buf.set_utf8_char(0, invalid_char)
+
+}
+
+///|
+test "set_utf16be_char with surrogate pairs" {
+  let buf = FixedArray::make(4, b'\x00')
+  // Test surrogate pair encoding for a supplementary plane character (U+10437)
+  let c = '\u{10437}'
+  let len = buf.set_utf16be_char(0, c)
+  inspect!(len, content="4")
+  // Check the generated bytes for correct UTF-16BE encoding
+  // High surrogate: D801, Low surrogate: DC37
+  inspect!(buf[0], content="b'\\xD8'")
+  inspect!(buf[1], content="b'\\x01'")
+  inspect!(buf[2], content="b'\\xDC'")
+  inspect!(buf[3], content="b'\\x37'")
+}
+
+///|
+test "panic set_utf16be_char with out of range code point" {
+  let buf = FixedArray::make(4, b'\x00')
+  ignore(buf.set_utf16be_char(0, Char::from_int(0x110000)))
+}
+
+///|
+test "Bytes::makei with non-positive length" {
+  let bytes = Bytes::makei(0, fn(_i) { b'\x00' })
+  inspect!(bytes, content="b\"\"")
+  let bytes2 = Bytes::makei(-1, fn(_i) { b'\x00' })
+  inspect!(bytes2, content="b\"\"")
+}