fix(statistics): add probability() function

[tysoncung]

Problem

Issue #105 requested a probability() function in statistics.py that computes favorable_outcomes / possible_outcomes and returns a float approximation — e.g. the probability of rolling a 4 on a die is probability(1, 6) → 0.1666...

Solution

Added probability(favorable_outcomes, possible_outcomes) with:

• Straightforward ratio calculation returning a float
• ValueError guard when possible_outcomes == 0
• ValueError guard when either argument is negative
• Full docstring following the project convention

Files Changed

• simple_equ/economics/statistics.py — added probability() function

Verification

from simple_equ.economics.statistics import probability

probability(1, 6)  # ≈ 0.1667 — rolling a specific side on a die
probability(3, 6)  # 0.5 — rolling an even number
probability(0, 6)  # 0.0
probability(6, 6)  # 1.0

Closes #105

[antfullstack]

Thank you very mush for your contribution! I really appreciate the error handling considerations and structure.