Fix discrete construction for real functions on complex domain

[tobydriscoll]

In Thiele discrete construction, values of r may be complex if nodes are complex, even if given values are real.

[github-actions]

Benchmark Results

Ratios above 1 mean this PR is slower than main.

	main	5a3d83e...	main / 5a3d83e...
approximate/aaa/abs_circle	0.0461 ± 0.0061 s	0.0466 ± 0.0019 s	0.99 ± 0.14
approximate/aaa/exp_interval	0.142 ± 0.027 ms	0.142 ± 0.025 ms	1 ± 0.26
approximate/aaa/tanh_steep	1.64 ± 0.063 ms	1.64 ± 0.057 ms	1 ± 0.052
approximate/thiele/abs_circle	4.97 ± 0.047 ms	4.98 ± 0.054 ms	0.997 ± 0.014
approximate/thiele/exp_interval	0.0981 ± 0.0054 ms	0.0987 ± 0.0052 ms	0.993 ± 0.076
approximate/thiele/tanh_steep	0.244 ± 0.014 ms	0.246 ± 0.013 ms	0.995 ± 0.077
approximate_discrete/aaa/abs_shift	4.06 ± 0.41 ms	4.11 ± 0.064 ms	0.989 ± 0.1
approximate_discrete/aaa/sin_recip	1.37 ± 0.14 ms	1.38 ± 0.032 ms	0.993 ± 0.1
approximate_discrete/aaa/tanh_steep	12.2 ± 1.5 ms	12.2 ± 0.73 ms	1 ± 0.14
approximate_discrete/thiele/abs_shift	0.27 ± 0.025 ms	0.283 ± 0.023 ms	0.955 ± 0.12
approximate_discrete/thiele/sin_recip	0.14 ± 0.015 ms	0.149 ± 0.013 ms	0.936 ± 0.13
approximate_discrete/thiele/tanh_steep	0.934 ± 0.096 ms	0.958 ± 0.081 ms	0.975 ± 0.13
evaluate/bary_vector	0.139 ± 0.0062 ms	0.138 ± 0.0069 ms	1.01 ± 0.068
evaluate/thiele_vector	0.108 ± 0.0005 ms	0.108 ± 0.00033 ms	1 ± 0.0056
poles/thiele	0.425 ± 0.021 ms	0.426 ± 0.015 ms	0.998 ± 0.06
time_to_load	0.91 ± 0.0043 s	0.899 ± 0.0095 s	1.01 ± 0.012

Benchmark Plots

Plots have been uploaded as an artifact to this workflow run
("Actions" -> this run -> "Artifacts" at the bottom).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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