Buffered CurveMap

[lucasprocessi]

Hi,
it seems that whenever I try to buffer a CurveMap, I always get the original non-mapped zero rates.

For instance, in those tests bellow:

@testset "Buffered CurveMap" begin
    
    flat_curve = InterestRates.IRCurve(
        "flat", InterestRates.Actual360(), InterestRates.SimpleCompounding(), InterestRates.StepFunction(),
        Date(2021,1,1), [1], [0.1]
    )
    @test InterestRates.zero_rate(flat_curve, Date(2022,1,1)) ≈ 0.1

    map_curve = InterestRates.CurveMap("mapped", (r,m) -> r+0.05, flat_curve)
    @test InterestRates.zero_rate(map_curve, Date(2022,1,1)) ≈ 0.15

    buffered_curve = InterestRates.BufferedIRCurve(map_curve)
    @test InterestRates.zero_rate(buffered_curve, Date(2022,1,1)) ≈ 0.15

end

... last test fails.

Buffered CurveMap: Test Failed at /home/InterestRates/test/runtests.jl:646
  Expression: InterestRates.zero_rate(buffered_curve, Date(2022, 1, 1)) ≈ 0.15
   Evaluated: 0.1 ≈ 0.15