### **User description**
Related to #44956
Add manifest-based data loading path for optional fields in
`cache_opt_field_memory_v2`. When a manifest file is provided in the
config, the function now retrieves field data directly from the manifest
using `GetFieldDatasFromManifest` instead of reading from segment insert
files. This enables storage v2 compatibility for building indexes with
optional fields.
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### **PR Type**
Enhancement
___
### **Description**
- Add manifest-based data loading for optional fields in index building
- Support storage v2 compatibility via `GetFieldDatasFromManifest`
function
- Enable PK isolation optional field handling without segment insert
files
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Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>
d3b15ac136