fix: Exercise 11.3.2 — multiplication/scaling do not preserve majorization

[Chessing234]

Summary

• MajorizesOn.of_add is true: if g ≤ f on I, then g+h ≤ f+h on I by add_le_add_right.
• MajorizesOn.of_mul is false: on Icc 0 1, take f ≡ 1, g ≡ 0, h ≡ -1. Then g ≤ f, but g*h ≡ 0 and f*h ≡ -1, so g*h ≰ f*h.
• MajorizesOn.of_smul is false for the same reason with scalar c = -1 (negative scaling reverses the inequality).

Test plan

• CI / lake build Analysis/Section_11_3.lean