Bugfix for FluxWeight and MeVPrtl

[VCLanNguyen]

1. Fix a bug in MeVPrtl: BNBKaonGen incorrectly label boone ntuple as dk2nu format. Updated to it simple flux format. This would prevent Flux Weight tools to to crash when inputting MeVPrtl files.
2. Add a feature in Flux Weight tools: to pick up neutrino energy from MCTruth instead if flux.nenergyn == -1.
   In MeVPrtl, by default, MCFlux neutrino energy is filled as -1 since not every meson in flux file would result in a neutrino. It instead computes an equivalent neutrino energy and saves it as MCTruth.
   This change should not impact the neutrino workflow since every meson results in a neutrino, and MCFlux flux.nenergyn should always be filled.

Description

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[jicrespo]

Please see the comments below.

[kjplows]

Hi @jicrespo and @VCLanNguyen , is this branch ready for CI? Thanks

[kjplows]

trigger build LArSoft/lar*@LARSOFT_SUITE_v10_14_02_01 SBNSoftware/sbndaq-artdaq-core@v1_10_06 SBNSoftware/sbncode@v10_14_02_01 SBNSoftware/sbn*@SBN_SUITE_v10_14_02_01

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⚠️ CI build for ICARUS Warning at phase ci_tests ICARUS on slf7 for e26:prof - ignored warnings for build -- details available through the CI dashboard

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