Cherry-pick from master, modified some files since branching
pr: #29858
See also #29803
This PR:
- Add trace span for LoadIndex & LoadFieldData in segment loader
- Add TraceCtx parameter for Index.Load in segcore
- Add span for ReadFiles & Engine Load for Memory/Disk Vector index
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Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>