perf: skip HexBytes allocation for int indexing (#257)

## Summary
Switch HexBytes32 int indexing to use bytes.__getitem__ while keeping
slice behavior on FasterHexBytes.

## Rationale
Avoids allocating FasterHexBytes on int indexing in a hot path without
changing results.

## Details
- Int keys now go through bytes.__getitem__; slices still return
FasterHexBytes.
- Added assertions for positive/negative int indexing parity with bytes.
- mypyc: evmspec/_new.cpython-313-x86_64-linux-gnu.so loaded during
tests.

## Testing
- ./.venv/bin/python -m pytest

Author: BobTheBuidler

evmspec/data/_main.py

@@ -410,7 +410,9 @@ def __getitem__(self, key: SupportsIndex) -> int: ...
     def __getitem__(self, key: slice) -> faster_hexbytes.HexBytes: ...
 
     def __getitem__(self, key: SupportsIndex | slice) -> int | faster_hexbytes.HexBytes:
-        return FasterHexBytes(self)[key]
+        if isinstance(key, slice):
+            return FasterHexBytes(self)[key]
+        return bytes.__getitem__(self, key)
 
     # TODO: keep the instance small and just task on the length for operations as needed
     # def __len__(self) -> Literal[32]:

tests/data/test_main.py

@@ -84,7 +84,10 @@ def test_hexbytes32_repr_hex_strip_hash() -> None:
 
 def test_hexbytes32_getitem() -> None:
     hb = HexBytes32(HEX32)
+    raw = bytes(hb)
     assert isinstance(hb[0], int)
+    assert hb[0] == raw[0]
+    assert hb[-1] == raw[-1]
     sliced = hb[:2]
     assert isinstance(sliced, FasterHexBytes)