Switch other backends to use new getter interface

[flimzy]

No description provided.

[codecov]

Codecov Report

Patch coverage: 60.00% and project coverage change: -0.12% ⚠️

Comparison is base (a79e11f) 79.33% compared to head (3ff3c4e) 79.21%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #764      +/-   ##
==========================================
- Coverage   79.33%   79.21%   -0.12%     
==========================================
  Files         165      165              
  Lines       12940    12954      +14     
==========================================
- Hits        10266    10262       -4     
- Misses       2235     2252      +17     
- Partials      439      440       +1     

Files Changed	Coverage Δ
driver/driver.go	100.00% <ø> (ø)
mockdb/gen/main.go	30.88% <ø> (ø)
x/fsdb/get.go	65.71% <52.94%> (-14.29%)	⬇️
x/memorydb/db.go	71.15% <55.55%> (-4.13%)	⬇️
db.go	94.43% <100.00%> (+0.26%)	⬆️

... and 2 files with indirect coverage changes

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