fix: handle UnicodeDecodeError on usernames with special characters

Fixes #2730. Usernames containing non-ASCII characters (e.g. 'Émile')
can trigger a UnicodeDecodeError inside the requests library during
redirect handling. This exception is not a subclass of
requests.exceptions.RequestException, so it escaped all existing
except blocks in get_response() and crashed the program.

Added a catch for UnicodeError (parent of both UnicodeDecodeError and
UnicodeEncodeError) so these sites are gracefully skipped instead of
crashing the entire scan.

Added regression tests in tests/test_unicode.py.

tests/test_unicode.py

@@ -0,0 +1,47 @@
+"""Tests for handling usernames with special/unicode characters."""
+
+from concurrent.futures import Future
+
+from sherlock_project.sherlock import get_response
+
+
+def _make_future_with_exception(exc):
+    """Create a Future that raises the given exception."""
+    future = Future()
+    future.set_exception(exc)
+    return future
+
+
+def test_get_response_handles_unicode_decode_error():
+    """Regression test for issue #2730.
+
+    Usernames with special characters (e.g. 'Émile') can trigger a
+    UnicodeDecodeError inside the requests library during redirect
+    handling. This must not crash the program.
+    """
+    future = _make_future_with_exception(
+        UnicodeDecodeError("utf-8", b"\xe9", 0, 1, "invalid continuation byte")
+    )
+    response, error_context, exception_text = get_response(
+        request_future=future,
+        error_type=["status_code"],
+        social_network="TestSite",
+    )
+    assert response is None
+    assert error_context == "Encoding Error"
+    assert "utf-8" in exception_text
+
+
+def test_get_response_handles_unicode_encode_error():
+    """UnicodeEncodeError should also be caught (subclass of UnicodeError)."""
+    future = _make_future_with_exception(
+        UnicodeEncodeError("ascii", "É", 0, 1, "ordinal not in range(128)")
+    )
+    response, error_context, exception_text = get_response(
+        request_future=future,
+        error_type=["status_code"],
+        social_network="TestSite",
+    )
+    assert response is None
+    assert error_context == "Encoding Error"
+    assert "ascii" in exception_text