meta/fdb: fix scan for many keys

[SandyXSD]

close #2801

The read transaction for scanning is retried, which leads to the huge number of scanned keys. In fdb, there is a 5s limit for the read transaction.

refs: https://forums.foundationdb.org/t/large-range-scans-avoid-5s-limit/292

[codecov-commenter]

Codecov Report

Base: 59.32% // Head: 59.33% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (504c2d1) compared to base (953a763).
Patch coverage: 83.33% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2824   +/-   ##
=======================================
  Coverage   59.32%   59.33%           
=======================================
  Files         140      140           
  Lines       24310    24324   +14     
=======================================
+ Hits        14423    14433   +10     
- Misses       8035     8038    +3     
- Partials     1852     1853    +1     

Impacted Files	Coverage Δ
pkg/meta/tkv_fdb.go	85.05% <83.33%> (-2.62%)	⬇️
pkg/meta/tkv_mem.go	86.61% <0.00%> (-0.71%)	⬇️
pkg/meta/sql.go	64.45% <0.00%> (-0.20%)	⬇️
pkg/meta/tkv.go	75.14% <0.00%> (+0.11%)	⬆️
pkg/vfs/writer.go	77.77% <0.00%> (+1.19%)	⬆️

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[T-TRz879]

I saw on the official website about the transaction solution that needs to run for a long time Long-running transactions