🐛 [RUM] fix loading measures conversion to nanoseconds

[BenoitZugmeyer]

Motivation

Load timings where not converted to nanosecond anymore

Changes

Make sure load timings are converted to nanosecond

Testing

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I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

Merging #490 into master will increase coverage by 0.33%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #490      +/-   ##
==========================================
+ Coverage   87.40%   87.73%   +0.33%     
==========================================
  Files          34       34              
  Lines        2112     2112              
  Branches      417      417              
==========================================
+ Hits         1846     1853       +7     
+ Misses        266      259       -7     

Impacted Files	Coverage Δ
packages/rum/src/rum.ts	89.92% <100.00%> (+3.87%)	⬆️
packages/logs/src/logger.ts	95.29% <0.00%> (+1.17%)	⬆️
packages/logs/src/loggerSession.ts	100.00% <0.00%> (+4.34%)	⬆️

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