fix(otlp-transformer): only use BigInt inside hrTimeToNanos()

[pichlermarc]

Which problem is this PR solving?

On older, unsupported browser runtimes the use of BigInt is causing some issues. (#4482, #4350)
We guard against the use of BigInt in the same file by falling back to to encoding the timestamp as a string if it is not defined, so this PR attempts to follow this pattern.

Fixes #4350

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Existing tests

[codecov]

Codecov Report

Merging #4484 (5441814) into main (44b0b29) will decrease coverage by 0.13%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

❗ Current head 5441814 differs from pull request most recent head ef7db01. Consider uploading reports for the commit ef7db01 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4484      +/-   ##
==========================================
- Coverage   92.55%   92.42%   -0.13%     
==========================================
  Files         315      330      +15     
  Lines        9375     9520     +145     
  Branches     2013     2031      +18     
==========================================
+ Hits         8677     8799     +122     
- Misses        698      721      +23     

Files	Coverage Δ
...ntal/packages/otlp-transformer/src/common/index.ts	100.00% <100.00%> (ø)

... and 16 files with indirect coverage changes