exercises(sum-of-multiples): implement

[ee7]

This is one of the first exercises for which a user can reasonably use a HashMap (as a set of integers). Put this exercise towards the end.

A u64 is sufficient for the maximum value of the sum of multiples when the limit is a u32. The maximum sum of multiples occurs for

const factors = [_]u32{1};
const limit = 4_294_967_295 // the maximum value of a u32

and the sum of integers from 1 (inclusive) to n (exclusive) is

n(n - 1) / 2

which is always less than n^2. So the sum from 1 to an integer less than 2^32 is always less than 2^64.

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To-do:

• configlet sync --docs Edit: Don't do this for now.
• Test sum that is larger than maximum value of a u32
• config.json: decide on exercise ordering after merging other exercises
• Final nits