Add @inline to some functions (#65)

This is dangerous and we should instead find the actual reason for the
inconsistency. I'll leave this as a draft for now and will look into it
more later. Since `Base.@assume_effects` requires Julia 1.8 this will
fail unit tests anyways.

Having these functions infer `:consistent` correctly by the compiler can
significantly help with optimization in the compiler, so eventually we
should try to make sure that most of QEDcore functionality has as many
effects inferred as possible.

Edit: I have removed the assumptions again because they are not safe to
make (at least not for all element types). We should come back to this
at a later point. For now, I have only added some `@inbounds`
statements.

src/particles/states.jl

@@ -1,71 +1,73 @@
-function _booster_fermion(mom::AbstractFourMomentum, mass::Real)
+@inline function _booster_fermion(mom::AbstractFourMomentum, mass::Real)
     return (slashed(mom) + mass * one(DiracMatrix)) / (sqrt(abs(getT(mom)) + mass))
 end
 
-function _booster_antifermion(mom::AbstractFourMomentum, mass::Real)
+@inline function _booster_antifermion(mom::AbstractFourMomentum, mass::Real)
     return (mass * one(DiracMatrix) - slashed(mom)) / (sqrt(abs(getT(mom)) + mass))
 end
 
 function QEDbase.base_state(
     particle::Fermion, ::Incoming, mom::AbstractFourMomentum, spin::AbstractDefiniteSpin
 )
     booster = _booster_fermion(mom, mass(particle))
-    return BiSpinor(booster[:, QEDbase._spin_index(spin)])
+    return BiSpinor(@inbounds booster[:, QEDbase._spin_index(spin)])
 end
 
 function QEDbase.base_state(
     particle::Fermion, ::Incoming, mom::AbstractFourMomentum, spin::AllSpin
 )
     booster = _booster_fermion(mom, mass(particle))
-    return SVector(BiSpinor(booster[:, 1]), BiSpinor(booster[:, 2]))
+    return SVector(BiSpinor(@inbounds booster[:, 1]), BiSpinor(@inbounds booster[:, 2]))
 end
 
 function QEDbase.base_state(
     particle::AntiFermion, ::Incoming, mom::AbstractFourMomentum, spin::AbstractDefiniteSpin
 )
     booster = _booster_antifermion(mom, mass(particle))
-    return AdjointBiSpinor(BiSpinor(booster[:, QEDbase._spin_index(spin) + 2])) * GAMMA[1]
+    return AdjointBiSpinor(BiSpinor(@inbounds booster[:, QEDbase._spin_index(spin) + 2])) *
+           (@inbounds GAMMA[1])
 end
 
 function QEDbase.base_state(
     particle::AntiFermion, ::Incoming, mom::AbstractFourMomentum, spin::AllSpin
 )
     booster = _booster_antifermion(mom, mass(particle))
     return SVector(
-        AdjointBiSpinor(BiSpinor(booster[:, 3])) * GAMMA[1],
-        AdjointBiSpinor(BiSpinor(booster[:, 4])) * GAMMA[1],
+        AdjointBiSpinor(@inbounds BiSpinor(booster[:, 3])) * (@inbounds GAMMA[1]),
+        AdjointBiSpinor(@inbounds BiSpinor(booster[:, 4])) * (@inbounds GAMMA[1]),
     )
 end
 
 function QEDbase.base_state(
     particle::Fermion, ::Outgoing, mom::AbstractFourMomentum, spin::AbstractDefiniteSpin
 )
     booster = _booster_fermion(mom, mass(particle))
-    return AdjointBiSpinor(BiSpinor(booster[:, QEDbase._spin_index(spin)])) * GAMMA[1]
+    return AdjointBiSpinor(BiSpinor(@inbounds booster[:, QEDbase._spin_index(spin)])) *
+           (@inbounds GAMMA[1])
 end
 
 function QEDbase.base_state(
     particle::Fermion, ::Outgoing, mom::AbstractFourMomentum, spin::AllSpin
 )
     booster = _booster_fermion(mom, mass(particle))
     return SVector(
-        AdjointBiSpinor(BiSpinor(booster[:, 1])) * GAMMA[1],
-        AdjointBiSpinor(BiSpinor(booster[:, 2])) * GAMMA[1],
+        AdjointBiSpinor(BiSpinor(@inbounds booster[:, 1])) * (@inbounds GAMMA[1]),
+        AdjointBiSpinor(BiSpinor(@inbounds booster[:, 2])) * (@inbounds GAMMA[1]),
     )
 end
 
 function QEDbase.base_state(
     particle::AntiFermion, ::Outgoing, mom::AbstractFourMomentum, spin::AbstractDefiniteSpin
 )
     booster = _booster_antifermion(mom, mass(particle))
-    return BiSpinor(booster[:, QEDbase._spin_index(spin) + 2])
+    return BiSpinor(@inbounds booster[:, QEDbase._spin_index(spin) + 2])
 end
 
 function QEDbase.base_state(
     particle::AntiFermion, ::Outgoing, mom::AbstractFourMomentum, spin::AllSpin
 )
     booster = _booster_antifermion(mom, mass(particle))
-    return SVector(BiSpinor(booster[:, 3]), BiSpinor(booster[:, 4]))
+    return SVector(BiSpinor(@inbounds booster[:, 3]), BiSpinor(@inbounds booster[:, 4]))
 end
 
 function _photon_state(pol::AllPolarization, mom::AbstractFourMomentum)