minor metrics handling optimizations

[ays7]

Minor metrics handling optimizations:

• avoid few unnecessary copies
• avoid empty exports with no data points

[codecov]

Codecov Report

Merging #1890 (711b2ba) into main (9197bf3) will increase coverage by 0.07%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1890      +/-   ##
==========================================
+ Coverage   85.71%   85.78%   +0.07%     
==========================================
  Files         171      171              
  Lines        5241     5243       +2     
==========================================
+ Hits         4492     4497       +5     
+ Misses        749      746       -3     

Impacted Files	Coverage Δ
sdk/src/metrics/state/metric_collector.cc	92.86% <100.00%> (+0.55%)	⬆️
sdk/src/metrics/state/temporal_metric_storage.cc	98.22% <100.00%> (ø)
ext/src/http/client/curl/http_client_curl.cc	81.44% <0.00%> (+1.14%)	⬆️

[lalitb]

LGTM. Can you fix the formatting so that the CI is successful.

[ays7]

@lalitb thanks for the ref -- missed that format script.
FYI: i took care of my mods, but the format appears to be violated in about a dozen or 2 of files in the repo...

[lalitb]

FYI: I took care of my mods, but the format appears to be violated in about a dozen or 2 of files in the repo...

This shouldn't happen if you are using clang-format v10.0. Anyway, the changes looks good now, as CI is successful. Thanks.