Add tests cases with infinite bounds

[mtanneau]

Test that edge cases such as

• MOI.LessThan(Inf)
• MOI.GreaterThan(-Inf)
• MOI.Interval(l, Inf), MOI.Interval(-Inf, u), MOI.Interval(-Inf, Inf)
  are properly handled.

A typical edge case:

m = XXX.Optimizer()
x = MOI.add_variable(m)

# Even though the line below will be interpreted as `x >= 0`,
# it should return an `MOI.ConstraintIndex{MOI.SingleVariable, MOI.Interval{Float64}}`
c = MOI.add_constraint(m, MOI.SingleVariable(x), MOI.Interval(0,0, Inf))
@test isa(c, MOI.ConstraintIndex{MOI.SingleVariable, MOI.Interval{Float64}})

# The constraint index should be valid
@test MOI.is_valid(m, c)

The goal of testing such edge cases would be to ensure that

• The MOI wrapper handles infinite values (as per the docs)
• Constraint indices are properly tracked

[mtanneau]

My main reason is that I was passing MOI tests, but raising errors when trying to integrate with Coluna.

Coluna appears to use MOI.Interval(lb, Inf) a lot.
cc @guimarqu