This PR splits sealed segment to chunked data to avoid unnecessary
memory copy and save memory usage when loading segments so that loading
can be accelerated.
To support rollback to previous version, we add an option
`multipleChunkedEnable` which is false by default.
Signed-off-by: sunby <sunbingyi1992@gmail.com>
https://github.com/milvus-io/milvus/issues/35112
This pr would not affect milvus functionality by now.
It implments a Chunk memory layout that looks like
```
VariableColumn
|offset|offset|offset|
|data|data|data|
```
We maybe move offsets to the beginning and add null bitmaps later but
not in this PR.
And mmap test will also be added in another PR.
---------
Signed-off-by: sunby <sunbingyi1992@gmail.com>
