Clarify traveling wave solution for BBM-BBM is unphysical

[JoshuaLampert]

Thanks @pnavaro for pointing that out.
Closes #256.

[github-actions]

Benchmark Results (Julia v1.10)

Time benchmarks

	main	ac80577...	main / ac80577...
bbm_1d/bbm_1d_basic.jl - rhs!:	14 ± 0.34 μs	13.8 ± 0.31 μs	1.01 ± 0.034
bbm_1d/bbm_1d_fourier.jl - rhs!:	0.535 ± 0.0092 ms	0.533 ± 0.0094 ms	1 ± 0.025
bbm_bbm_1d/bbm_bbm_1d_basic_reflecting.jl - rhs!:	0.0809 ± 0.00042 ms	0.0808 ± 0.0004 ms	1 ± 0.0072
bbm_bbm_1d/bbm_bbm_1d_dg.jl - rhs!:	0.0342 ± 0.00048 ms	0.0343 ± 0.00047 ms	0.999 ± 0.02
bbm_bbm_1d/bbm_bbm_1d_relaxation.jl - rhs!:	28.7 ± 0.86 μs	27.4 ± 0.5 μs	1.05 ± 0.037
bbm_bbm_1d/bbm_bbm_1d_upwind_relaxation.jl - rhs!:	0.0488 ± 0.00054 ms	0.0485 ± 0.00061 ms	1.01 ± 0.017
hyperbolic_serre_green_naghdi_1d/hyperbolic_serre_green_naghdi_dingemans.jl - rhs!:	4.26 ± 0.04 μs	4.29 ± 0.04 μs	0.993 ± 0.013
kdv_1d/kdv_1d_basic.jl - rhs!:	1.43 ± 0.011 μs	1.42 ± 0.02 μs	1.01 ± 0.016
kdv_1d/kdv_1d_implicit.jl - rhs!:	1.42 ± 0.02 μs	1.42 ± 0.021 μs	1 ± 0.02
serre_green_naghdi_1d/serre_green_naghdi_well_balanced.jl - rhs!:	0.2 ± 0.009 ms	0.203 ± 0.0085 ms	0.986 ± 0.061
svaerd_kalisch_1d/svaerd_kalisch_1d_dingemans_relaxation.jl - rhs!:	0.147 ± 0.0038 ms	0.151 ± 0.005 ms	0.974 ± 0.041
time_to_load	2 ± 0.011 s	2 ± 0.0064 s	1 ± 0.0064

Memory benchmarks

	main	ac80577...	main / ac80577...
bbm_1d/bbm_1d_basic.jl - rhs!:	1 allocs: 4.12 kB	1 allocs: 4.12 kB	1
bbm_1d/bbm_1d_fourier.jl - rhs!:	1 allocs: 4.12 kB	1 allocs: 4.12 kB	1
bbm_bbm_1d/bbm_bbm_1d_basic_reflecting.jl - rhs!:	5 allocs: 1.17 kB	5 allocs: 1.17 kB	1
bbm_bbm_1d/bbm_bbm_1d_dg.jl - rhs!:	10 allocs: 8.62 kB	10 allocs: 8.62 kB	1
bbm_bbm_1d/bbm_bbm_1d_relaxation.jl - rhs!:	2 allocs: 8.25 kB	2 allocs: 8.25 kB	1
bbm_bbm_1d/bbm_bbm_1d_upwind_relaxation.jl - rhs!:	2 allocs: 8.25 kB	2 allocs: 8.25 kB	1
hyperbolic_serre_green_naghdi_1d/hyperbolic_serre_green_naghdi_dingemans.jl - rhs!:	0 allocs: 0 B	0 allocs: 0 B
kdv_1d/kdv_1d_basic.jl - rhs!:	0 allocs: 0 B	0 allocs: 0 B
kdv_1d/kdv_1d_implicit.jl - rhs!:	0 allocs: 0 B	0 allocs: 0 B
serre_green_naghdi_1d/serre_green_naghdi_well_balanced.jl - rhs!:	0.075 k allocs: 0.66 MB	0.075 k allocs: 0.66 MB	1
svaerd_kalisch_1d/svaerd_kalisch_1d_dingemans_relaxation.jl - rhs!:	0.042 k allocs: 0.315 MB	0.042 k allocs: 0.315 MB	1
time_to_load	0.153 k allocs: 14.5 kB	0.153 k allocs: 14.5 kB	1

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[coveralls]

Pull Request Test Coverage Report for Build 19463112123

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.552%

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Totals
Change from base Build 19433129167:	0.0%
Covered Lines:	2314
Relevant Lines:	2348

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💛 - Coveralls