improve how proptest errors are displayed

[folkertdev]

see #516 (comment)

failures are now rendered as

    thread 'f32::log::lanes_3' (1001) panicked at crates/test_helpers/src/lib.rs:149:5:
    Test failed: assertion failed: `(left == right)` 
      left: `[NaN (ffc00000), NaN (ffc00000), -1.7069013 (bfda7bbe)]`,
     right: `[NaN, NaN, -1.7069033]` at crates/test_helpers/src/lib.rs:374.
    minimal failing input: (
        [
            -4120549500000.0,
            inf,
            6.2068386e-14,
        ],
        [
            3.0238625e25,
            -1.0388e-38,
            54636652.0,
        ],
    )

Much more readable.

[calebzulawski]

Thanks! Looks good! Great use of track_caller.