TPC digitizer follow-ups to #16090 - #16121

This fixes stale chunked digit files when the number of TPC lanes changes and lets the multithreaded device accept --tpc-sector-seeding.

- The chunked digit merger reads every lane file in the directory, but each lane removed only its own file. After a run with more lanes or threads, the extra lane files stayed and their sectors were published twice.
- The first lane now also removes the files of lanes the run does not have; the multithreaded device removes all of them, as before.
- The file name and the cleanup are shared by both devices.
- --tpc-sector-seeding is now a common option; the multithreaded device always seeds per sector, so it accepts the option without effect.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

This moves code that the lane and the multithreaded TPC digitizer devices duplicated into TPCSectorDigitization.

- LaneDigitFileWriter writes the flushes of a sector to the chunked digit file of a lane, for both devices.
- sectorSeedingBaseSeed() selects the base seed of the per-sector seeding, on which equal digits of both devices rely.
- TPCDigitizerConditions::update() returns the drift velocity change instead of calling back; finaliseCCDB() returns nothing.
- The multithreaded device takes its sectors from the spec instead of the input headers.
- Dead helpers and unused includes are removed from the lane device.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

…B lock

This replaces the process-wide lock around the CDBInterface reads of the TPC digitizer by a calibration snapshot that one thread reads per timeframe.

- DigitizerCalibrations holds the gain, pedestal, noise, threshold, per-pad ion tail and common mode maps, a copy of the dead channel map and the CMC flag.
- TPCDigitizerConditions::update() reads it once per timeframe, after the other conditions; both devices pass it to their digitizers, which only read it.
- Digitizer::init() no longer reads the CDBInterface or takes a lock; a digitizer used on its own reads a snapshot itself.
- The dead channel map is copied once per timeframe instead of once per sector.
- The one-time settings report moved into the snapshot read, so no worker thread reads the CDBInterface.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>