Allow specify schema in capnproto's stream interface

[lixin-wei]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @lixin-wei, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request extends the CapnProto integration to support explicit schema specification when performing stream-based read and write operations. This enhancement provides greater control and flexibility for serialization and deserialization, while also improving build compatibility with various CapnProto library versions through a CMake update.

Highlights

• CMake Compatibility: Updated CMakeLists.txt to ensure compatibility with older CapnProto installations by conditionally linking CapnProto::capnpc or capnpc.
• Stream Read with Schema: Added a new read function overload in rfl/capnproto/read.hpp that allows specifying a schema when deserializing CapnProto messages from an std::istream.
• Stream Write with Schema: Introduced a new write function overload in rfl/capnproto/write.hpp that enables specifying a schema when serializing objects to an std::ostream.

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[gemini-code-assist]

Code Review

This pull request introduces support for specifying a schema when reading from and writing to streams with the Cap'n Proto interface. This is a useful feature for performance. The changes also include a modification to CMakeLists.txt to improve compatibility with older versions of Cap'n Proto.

My review includes a suggestion to refactor the CMake script to reduce code duplication. More importantly, I've identified significant performance and memory usage issues in the new stream handling functions in read.hpp and write.hpp. Both functions buffer the entire stream content in memory, which can be problematic for large data. I've provided detailed suggestions on how to implement true streaming by using kj::InputStream and kj::OutputStream wrappers for std::istream and std::ostream respectively. Addressing these points will make the new functionality much more robust and efficient.

[liuzicheng1987]

@lixin-wei , thanks for your contribution!