[UBSAN] HGCalVFECompressionImpl: shift exponent 4294967295

[smuzaffar]

We have few UBSAN runtime errors [a]. This happens when exponent (const uint32_t exponent = bitlen - mantissaBits_;) is 1 which causes exponent-2 to become 4294967295 at https://github.com/cms-sw/cmssw/blob/master/L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc#L53

@cms-sw/l1-l2 , can you please look in this code and provide a fix ?

[a] https://cmssdt.cern.ch/SDT/jenkins-artifacts/ubsan_logs/CMSSW_14_2_X_2024-10-20-2300/logs/19/19a823aeb7adc34647332f165d28b627/log

23634.0/step2:L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc:53:42: runtime error: shift exponent 4294967295 is too large for 64-bit type 'long unsigned int'
24034.0/step2:L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc:53:42: runtime error: shift exponent 4294967295 is too large for 64-bit type 'long unsigned int'
24834.0/step2:L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc:53:42: runtime error: shift exponent 4294967295 is too large for 64-bit type 'long unsigned int'
24834.911/step2:L1Trigger/L1THGCal/src/HGCalVFECompressionImpl.cc:53:42: runtime error: shift exponent 4294967295 is too large for 64-bit type 'long unsigned int'