Include last data point in linear system solve for interpolating weights

[cgeoga]

A slightly funny one-char PR. But on the main branch right now, the linear system that is set up to compute the weights for the interpolating equations effectively treats the last function value (y[end]) as being zero instead of using the value, which can create some funny incorrect answers downstream.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/interpolation.jl	100.00% <100.00%> (ø)

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[kylebeggs]

@cgeoga thanks so much for this PR! I added a test and refactored the line to use more idiomatic Julia.