deprecating legacy schema codec

The schema codec in https://github.com/4paradigm/OpenMLDB/blob/ff7e8acf21ead1f9734eef59ac3521adb05dff2e/hybridse/include/codec/fe_schema_codec.h#L34-L110

is not real serialization solution for schemas. It

1. Not extendable. complex data type like #3680 is not possible without breaking change, it can not represent map type in single byte.
2. Hardware dependent. Endianness and primitive type size vary on different platform
3. Lack of type safety check, and is error prone.

## Solution ?

The issue points to hybridse/include/codec/fe_schema_codec.h lines 34-110, which contains the legacy schema codec. First, examine the current codec implementation to understand its limitations. Then, look for any existing serialization solutions in the codebase that could replace it. The goal is to design a new, extensible, platform-independent, and type-safe schema serialization method, but the issue does not specify a concrete solution or next steps.

索引モデルが issue の本文から書いたものです。