Resolved client-server interdependence when running a Murfey server

[tieneupin]

Partially resolves issue #446 .

murfey.client.contexts.tomo._midpoint was imported and used once in murfey.server.__init__. This causes the modules in murfey.client to be initialised, leading to a dependency chain where the client-side dependencies have to be installed just to run the server modules.

By duplicating the _midpoint function in murfey.server.__init__, this breaks that import chain.

EDIT: A better solution has been to move the midpoint() function over to murfey.util.__init__, which breaks that import chain

[codecov]

Codecov Report

Attention: Patch coverage is 30.76923% with 9 lines in your changes missing coverage. Please review.

Project coverage is 27.04%. Comparing base (19f2f31) to head (6988807).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #447      +/-   ##
==========================================
+ Coverage   27.03%   27.04%   +0.01%     
==========================================
  Files          75       76       +1     
  Lines       10188    10190       +2     
  Branches     1345     1345              
==========================================
+ Hits         2754     2756       +2     
  Misses       7344     7344              
  Partials       90       90              

[tieneupin]

Closed because it is already being looked at in the newer PR (#448).