Implement pipe()

Implement solve(fn_exprs, initial) where fn_exprs is a list of
lambda expression strings and initial is the starting value.

Apply each function left-to-right, passing the result of each to the next
(like Unix pipes, or functools.reduce).

solve(['lambda x: x + 1', 'lambda x: x * 2', 'lambda x: x - 3'], 5)
→ ((5 + 1) * 2) - 3 → 9

Rules

• Compile each expression string with eval(expr).
• If fn_exprs is empty, return initial unchanged.