ffi: Add WIP Serializer class for the next IR stream format.

[LinZhihao-723]

Description

When migrating to the next IR stream format, there are two important differences:

1. The serialization is no longer stateless in the next IR format. The stream has to maintain a schema tree across the entire IR stream.
2. In the current IR format, bytes can be written into the IR buffer in the same order as encoded: first encoded variables, then logtype, and finally timestamp. This is not true in the next IR format. For structured key-value pairs, the overall packet of a new record would be: [new_schema_tree_nodes, keys, values]. Each sub-packet has to be encoded in a separate buffer and merged into one after the entire record is processed. This means we need more than one internal buffer during the serialization, even though only the final merged buffer is exposed to the upper layer APIs.

To adapt to these changes, we wrap all the necessary data structures into a new class named Serializer to keep track of the states, as well as maintain necessary data structures. In details:

• It maintains an underlying schema tree for the stream.
• It maintains all the necessary internal buffers for serialization. These internal buffers are private members. In the future PRs, serialization methods will be added as member functions and they will have direct access to these buffers.
• It provides an API to access the view of the serialized IR buffer (containing serialized bytes).

Note: this class is designed to provide serialization functionalities only. The upper-level caller should be responsible for writing the serialized bytes into IO streams properly. In addition, it doesn't provide a call to terminate the IR stream. The upper-level caller should decide when to terminate the stream by append clp::ffi::ir_stream::cProtocol::Eof at the end of the stream.

Validation performed

• Added a unit test case to ensure the serializer can be successfully created with the preamble section serialized properly; also tested to ensure it can properly serialize a UTC offset change.
• Passsed clang-tidy checks for the Serializer implementation.
• Didn't execute clang-tidy against the unit test file since it is not synchronized with the latest coding guideline.

[gibber9809]

LGTM. How about "ffi: Add Serializer class for new IR stream format." for the title?

[kirkrodrigues]

LGTM. How about "ffi: Add Serializer class for new IR stream format." for the title?

How about a slight update:

ffi: Add WIP Serializer class for the next IR stream format.

[LinZhihao-723]

LGTM. How about "ffi: Add Serializer class for new IR stream format." for the title?

How about a slight update:

ffi: Add WIP Serializer class for the next IR stream format.

lgtm