Placement service lock optimisations and race condition fix

[elena-kolevska]

Description

This PR introduces a few placement service optimisations:

• Calculates the vnodes for all hosts outside of the placementTable lock
• Calculates the vnodes for a single host outside of lock when adding a host to the placement table (which is still done for backwards compatibility)

A race condition fix:

• The resetPlacementTables method was called without a lock from two places - on actor placement start and on reconnection to the placement service.

This PR It also clean ups the apiLevel parameter from the connectToServer method, because it's not used anymore.

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Unit tests passing
• End-to-end tests passing

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (007ccf5) 62.31% compared to head (3eab372) 62.32%.

Files	Patch %	Lines
pkg/actors/placement/placement.go	83.33%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7428      +/-   ##
==========================================
+ Coverage   62.31%   62.32%   +0.01%     
==========================================
  Files         240      240              
  Lines       22070    22077       +7     
==========================================
+ Hits        13752    13760       +8     
+ Misses       7178     7173       -5     
- Partials     1140     1144       +4     

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[elena-kolevska]

This is just a leftover cleanup from #7415