Tidying up Calorimeter Digitization random number seeding

Merged John Derek Chapman requested to merge jchapman/athena:CaloDigiRandomSeeding_master into master

This merge request aims to make the random seeding used in LAr and Tile Digitization as similar as possible to the seeding used in 21.0, while still being thread-safe.

In particular it fixes a bug introduced in !25992 (merged), where the random number stream was re-seeded every time LArTTL1Maker::computeNoise(...) was called rather than once per event.

FYI @jpanduro.

NB in 21.0 TileDigitsFromPulse, TileHittoRawChannel and TileDigitsMaker all shared a common random stream. If they were run in the same job in 21.0 this would cause interference between them (I don't think they were). Even after the changes in this merge request, the random streams will still be distinct in master.

Edited by John Derek Chapman

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