rust: add evmc-client binding

[axic]

This is a copy of #527.

[codecov[bot]]

Codecov Report

Merging #640 (34a5f67) into evmc-loader (c16008b) will not change coverage. The diff coverage is n/a.

@@             Coverage Diff              @@
##           evmc-loader     #640   +/-   ##
============================================
  Coverage        92.86%   92.86%           
============================================
  Files               23       23           
  Lines             3546     3546           
  Branches           375      375           
============================================
  Hits              3293     3293           
  Misses             144      144           
  Partials           109      109