chore: improves test coverage in ws-server package

[konstantinabl]

Description:

The goal of this PR is to improve the test coverage of the ws-server package, more precisely of the three following files:

• connectionLimiter.ts
• wsMetricRegistry.ts
• pollerService.ts

Related issue(s):

Fixes #3908 #3926 #3927

Notes for reviewer:

https://github.com/hiero-ledger/hiero-json-rpc-relay/pull/3928/files#diff-42934bb457ef270c151411688f1ae741d52945651e9c7b74bfe881e815da0c78R30
This change was done, so we can easily test the shouldRateLimitOnMethod method. If the IPRateLimitService is created in the connectionLimiter class itself, its pretty hard to mock it and test the method properly

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[github-actions]

Test Results

 20 files  ±0  277 suites  +1   18m 1s ⏱️ -10s
702 tests +1  697 ✅ +2  5 💤 ±0  0 ❌  - 1 
718 runs  +1  713 ✅ +2  5 💤 ±0  0 ❌  - 1 

Results for commit 2c53310. ± Comparison against base commit 8870d23.

♻️ This comment has been updated with latest results.

[quiet-node]

LGTM! Nice set of tests! Great work as always!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

@@            Coverage Diff             @@
##             main    #3928      +/-   ##
==========================================
+ Coverage   86.82%   88.18%   +1.36%     
==========================================
  Files          87       87              
  Lines        5086     5037      -49     
  Branches     1038     1020      -18     
==========================================
+ Hits         4416     4442      +26     
+ Misses        395      330      -65     
+ Partials      275      265      -10     

Flag	Coverage Δ
config-service	95.78% <ø> (+1.74%)	⬆️
relay	81.27% <ø> (+0.06%)	⬆️
server	80.81% <ø> (ø)
ws-server	83.86% <100.00%> (+22.85%)	⬆️

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

Files with missing lines	Coverage Δ
...ackages/ws-server/src/metrics/connectionLimiter.ts	85.33% <100.00%> (+50.26%)	⬆️
packages/ws-server/src/service/pollerService.ts	83.78% <ø> (+13.51%)	⬆️

... and 12 files with indirect coverage changes

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