MuonCablingTools: cleanup/optimization of DBline class

Cleanup and optimization of the DBline class that is used to parse RPC text configurations (usually read from COOL):

• Add a unit test for the DBline class that will make future changes easier to validate.
• Remove the obsolete I/O formatters (hex, dec, oct) that were using excessive amounts of news. These functions were not used anymore and the code comments said those are obsolete and replaced by the equivalent dbhex, etc. version. Also delete the now obsolete setdbfmtflag to switch between the old/new formatters.
• Update the documentation. It said floats are supported but that was never the case.
• Delete unsupported stream operators for floating point types. Also remove operators for pointer types (why would anybody use those?).
• Use std::string_view where possible.
• Use delegating constructor to avoid copy&paste.
• Remove internal "store" that was not being used.
• Use std::getline instead of get to read full line. This is a slight change of behavior as now the terminating newline will be part of the data. In practice this makes no difference as any whitespace is ignored via the isspace check already.
• General code cleanup and improvements.
• Also make the necessary adjustments in RPC_CondCabling.

👋 These are in principle all technical changes. An additional careful look by a muon expert (cc @jojungge @nkoehler) could be useful though.