ITS: simplify constants + mathutils

[f3sch]

removes custom definitions of constants in favour of o2-wide ones.
also tries to simplify some math expressions.

[github-actions]

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[alibuild]

Error while checking build/O2/fullCI_slc9 for 31ac10a at 2025-06-10 16:23:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/14383-slc9_x86-64/0/ALICE3/TableProducer/OTF/onTheFlyTracker.cxx:811:114: error: 'o2::its::constants::math' has not been declared
ninja: build stopped: subcommand failed.

Full log here.

[mpuccio]

Looks good, maybe there is only one small thing that was not really protected before but we could do better now.

[alibuild]

Error while checking build/O2/fullCI_slc9 for 5d3f3f1 at 2025-06-11 00:00:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/14383-slc9_x86-64/0/ALICE3/TableProducer/OTF/onTheFlyTracker.cxx:811:114: error: 'o2::its::constants::math' has not been declared
ninja: build stopped: subcommand failed.

Full log here.

[f3sch]

@mconcas @fprino I think this is ready to go if you approve