[SIGMON-179] Reading RQ U_DIODE_RQx signals

Context

• task: https://its.cern.ch/jira/browse/SIGMON-179

What was done

• DiodeLeadResistanceQuery refactored, method for obtaining metadata for voltage queries extracted (_get_u_query_metadata)
• DiodeLeadResistanceRqQuery created with its own _get_u_query_metadata method that implements 'correct reading of U_DIODE_RQx signals'

TODO

• tasks created to clarify and simplify metadata: https://its.cern.ch/jira/browse/SIGMON-238
• task created to correctly handle multi-circuit queries: https://its.cern.ch/jira/browse/SIGMON-239

QA

• http://sonar.cern.ch/project/issues?branch=SIGMON-179_reading_u_diode_rqx&id=lhc-sm-api&resolved=false (pushing coverage to sonar is fixed on a branch which is still in review)
• code was unit tested
• notebooks were executed: https://gitlab.cern.ch/LHCData/lhc-sm-hwc/-/jobs/17324476

Review objectives

• assessment of code functionality
• assessment of code quality
• identifying potential refactorings / logic common to other projects
• knowledge sharing
• getting help to understand a piece of code