Replace tokio::spawn with direct async future in read_all_fileinfo_full_wait.
join_all already provides concurrency, so tokio::spawn adds unnecessary
task creation and scheduling overhead.
Changes:
- Remove tokio::spawn from metadata fanout futures
- Update result handling for direct future results
Expected impact: 16-32us reduction per GET request.
Closesrustfs/backlog#769
Co-Authored-By: heihutu <[email protected]>