fix: proc: Keep same muon data ordering on output

Since 2023, the muon processor had been writing all the first muons in
the packet ahead of the all the second muons existing in the BX. Now the
 same incoming order is kept for the output.

Because BxData now holds both muons in the BX, the maximum amount
comported is doubled (eight rather than four).

Fixes issue #63 (wrong muon sorting).