chore(core): parse legacy rate limit if new rate limit not exist

[harukatab]

Description

• Fixes WB-18710

What does the PR do? Include a concise description of the PR contents.

• when the backend sends back only the old rate limit headers X-RateLimit-Remaining, it uses that without erroring out
• The old rate limit doesn't send back X-RateLimit-Reset so it defaults to 0
• if the backend sends back the new rate limit headers RateLimit-Remaining & RateLimit-Reset, SDK uses that values over legacy values

Testing

• added unit test

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 75.83%. Comparing base (e9cb82d) to head (085417b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7614      +/-   ##
==========================================
+ Coverage   74.27%   75.83%   +1.55%     
==========================================
  Files         500      500              
  Lines       55642    54048    -1594     
==========================================
- Hits        41328    40987     -341     
+ Misses      13907    12651    -1256     
- Partials      407      410       +3     

Flag	Coverage Δ
func	41.43% <ø> (+<0.01%)	⬆️
system	63.48% <45.45%> (+0.01%)	⬆️
unit	56.39% <90.90%> (+1.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
core/internal/api/ratelimitheaders.go	91.30% <90.90%> (+6.68%)	⬆️

... and 101 files with indirect coverage changes

[dmitryduev]

Looks great!
Could you please fix linting? Kind of strange though, should have been caught by the pre-push hook (https://github.com/wandb/wandb/blob/main/CONTRIBUTING.md#linting-the-code)