Improve performance of updating nano_enrollments host last seen timestamp under load

[mna]

#21340

Checklist for submitter

• Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes.
  See Changes files for more information.
• Added/updated tests
• Manual QA for all new/changed functionality

[codecov]

Codecov Report

Attention: Patch coverage is 74.44444% with 23 lines in your changes missing coverage. Please review.

Project coverage is 53.55%. Comparing base (6a26b89) to head (df52ee8).
Report is 50 commits behind head on main.

Files with missing lines	Patch %	Lines
server/mdm/nanomdm/storage/mysql/mysql.go	42.85%	16 Missing ⚠️
server/datastore/mysql/nanomdm_storage.go	36.36%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23896      +/-   ##
==========================================
- Coverage   63.14%   53.55%   -9.60%     
==========================================
  Files        1558     1561       +3     
  Lines      147877   148437     +560     
  Branches     3748     3748              
==========================================
- Hits        93384    79496   -13888     
- Misses      47102    62443   +15341     
+ Partials     7391     6498     -893     

Flag	Coverage Δ
backend	53.51% <74.44%> (-10.47%)	⬇️

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