Reject JSON input truncated at an embedded NUL - #245

loads('123\0garbage'), load() and Decoder() currently return 123, silently ignoring the NUL and everything after it. Refs #241, specifically the reported jts-8259-n_multidigit_number_then_00 compliance failure (123\0).

RapidJSON uses NUL as its end-of-input sentinel. After an otherwise successful parse, check the actual input length or the stream wrapper's EOF state. Report remaining input through the existing JSONDecodeError path, retaining the byte offset and the standard document-root error message. Escaped NULs in JSON strings remain valid.

Regression tests cover all six decoding routes, scalar/container documents, UTF-8 byte offsets, bytes/bytearray inputs, and stream chunk boundaries. This change does not alter the parse-flag dispatch addressed by #243.

Validation on macOS with CPython 3.11.5, using a locally built C++ extension:

• Before the fix: the 92 new cases produced 88 failures and 4 passes.
• After the fix: all 92 new cases pass. Full pytest tests -o addopts='' -q: 1029 passed, 17 skipped, 2 xfailed. The unchanged base passes its original suite: 937 passed, 17 skipped, 2 xfailed.
• python -m mypy.stubtest rapidjson, Python compilation of the modified test files, and git diff --check pass. The repository has no configured lint command.
• The prescribed Sphinx 8.2.3 doctest check runs 269 examples with one failure at docs/loads.rst:114, where the native-mode large integer is represented as 1.2345678901234568e+29 instead of 1.2345678901234566e+29. A separately built, unchanged checkout at 7337070f5bff88c8dc9803eded753f714c6fc1c0 reproduces the identical failure. Both runs also report the existing missing _static directory warning.

AI disclosure: OpenAI Codex generated and locally validated this patch and its tests. No separate human code review has been performed. Hosted CI, other Python versions/platforms, debug/free-threaded builds, sanitizers, and performance benchmarks have not been verified locally.