zstd_safe::DCtx::decompress_stream may result in UB

[vilgotf]

The decompress_stream method internally calls ZSTD_decompressStream which has the following note:

Note: when an operation returns with an error code, the zds state may be left in undefined state.
It's UB to invoke ZSTD_decompressStream() on such a state.
In order to re-use such a state, it must be first reset,
which can be done explicitly (ZSTD_DCtx_reset()),
or is implied for operations starting some new decompression job (ZSTD_initDStream, ZSTD_decompressDCtx(), ZSTD_decompress_usingDict())

This is not enforced by zstd-safe and is left for callers to handle. The method must either be unsafe or error/panic when called on undefined state.