fix(rust): Fix Display implementation of Duration

[MarcoGorelli]

It's currently off by a factor of 1_000, '20h' gets displayed as '72000000h' instead of '72000h'

Pulling some constants together and using those instead

I may well have some typos here, but I'm just going out - will fixup when I get back

[codspeed-hq]

CodSpeed Performance Report

Merging #15647 will not alter performance

_{Comparing MarcoGorelli:refactors (d103644) with main (37c6303)}

Summary

✅ 22 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.31%. Comparing base (81002ca) to head (d103644).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15647   +/-   ##
=======================================
  Coverage   81.30%   81.31%           
=======================================
  Files        1373     1373           
  Lines      176243   176254   +11     
  Branches     2544     2544           
=======================================
+ Hits       143302   143321   +19     
+ Misses      32458    32452    -6     
+ Partials      483      481    -2     

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[stinodego]

Thanks for the fix!