Make L1TopoByteStreamCnv thread-safe

The ByteStream converter L1TopoByteStreamCnv and specifically the tool it uses - L1TopoByteStreamTool - wasn't thread-safe and caused crashes reported in ATR-23935. Fix the code and further ensure thread-safety by moving it to const interfaces.

Details:

• stop overriding m_sourceIDs during execution of the tool's convert methods - configure them only once in initialize()
• remove class member m_fea and allocate it on the stack instead
• make all convert methods of the tool const
• move the converter to the AthConstConverter interface
• use ATH_MSG macros for messaging

Fixes ATR-23935