Add IMAGINE instrument definition and update MaskBTP

[jmborr]

Companion to #40825
EWM 14495

Description of work

Support for the IMAGINE instrument to the Mantid project by:

1. Adding a new instrument definition file (IMAGINE_Definition_2025_10_01.xml)
2. Updating the MaskBTP algorithm to support IMAGINE
3. Adding unit tests for the IMAGINE instrument in MaskBTPTest.py

To test:

ws = LoadEmptyInstrument(InstrumentName="IMAGINE", OutputWorkspace="imagine")
masked_banks = MaskBTP(Workspace=ws, Bank="11-18")
assert len(masked_banks) == 8 * 512 * 512

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