[C++] Streaming Deserialization Support For C++

[chaokunyang]

Feature Request

Add C++ stream deserialization support while preserving existing deserialize(const uint8_t*, size_t) and deserialize(Buffer&) APIs.

Is your feature request related to a problem? Please describe

Current C++ deserialization is buffer-only. Users integrating with gRPC/RPC streams need extra buffering and framing glue before calling Fory.

Design update (based on PR #3307)

Reference: #3307

1. API shape

• Keep current deserialize entrypoints unchanged.
• Introduce stream-backed buffer usage via ForyInputStream + Buffer so existing deserialize(Buffer&) path can consume stream input.
• No mandatory one-shot deserialize(std::istream&) API in this phase.

2. Stream abstraction

• Add fory::ForyInputStream (cpp/fory/util/stream.h) wrapping std::istream.
• ForyInputStreamBuf maintains a growable internal byte window and supports fill_buffer(min_bytes), consume, rewind, reader_index, and size queries.

3. Buffer/read integration

• Extend fory::Buffer with ensure_size(target_size, error) so reads can auto-fill from attached stream when needed.
• Update deserialization read paths (header, string, struct/object reads) to call ensure_size instead of assuming all bytes are already materialized.
• Keep pure in-memory hot path behavior unchanged when no stream is attached.

4. Object-boundary behavior

• Preferred mode is reusing one stream-backed Buffer across sequential deserializations from the same stream.
• No stream seek rewind requirement in this design; unread prefetched bytes stay in the stream buffer.

5. Error handling

• Premature EOF / short read is reported through existing Result<T, Error> with buffer/out-of-bound or invalid-data style errors.

6. Tests

• Add C++ stream tests for:
• tiny-fragmented reads,
• primitive/string/struct roundtrip,
• reference graph behavior,
• sequential multi-object decode from one stream,
• truncated stream error handling.

Describe alternatives you've considered

• Force callers to read full payload into memory first.
• Add only a one-shot stream API with seek rewind.

Additional context

Relevant files (PR #3307):

• cpp/fory/util/stream.h
• cpp/fory/util/buffer.h
• cpp/fory/serialization/serializer.h
• cpp/fory/serialization/stream_test.cc

[Anasyaseen92]

I would like to work on this issue, please assign it to me.