feat: allow user-specified stdin

[MilesCranmer]

This lets the user specify a specific IO object to read user input from, which by default is stdin, but could also be some other stream.

This fixes #370.

@rafaelcuperman sorry you haven't received a response from the VSCode extension team, I think they are just pretty busy. In the meantime I hope this helps with your issue! You would just specify input_stream=devnull when running on your system and it should avoid the hang.

[github-actions]

Benchmark Results

	master	4da6aa3...	master/4da6aa3163771a...
search/multithreading	21 ± 1.7 s	20 ± 1.9 s	1.05
search/serial	31.6 ± 0.39 s	32.1 ± 0.051 s	0.984
utils/best_of_sample	1.91 ± 1.6 μs	1.91 ± 1.6 μs	1
utils/check_constraints_x10	11.4 ± 2.9 μs	11.4 ± 2.9 μs	1
utils/compute_complexity_x10/Float64	2.07 ± 0.1 μs	2.11 ± 0.11 μs	0.981
utils/compute_complexity_x10/Int64	2.01 ± 0.11 μs	2.02 ± 0.11 μs	0.995
utils/compute_complexity_x10/nothing	1.47 ± 0.12 μs	1.49 ± 0.1 μs	0.986
utils/insert_random_op_x10	5.82 ± 1.9 μs	5.87 ± 1.8 μs	0.991
utils/next_generation_x100	0.417 ± 0.12 ms	0.445 ± 0.12 ms	0.938
utils/optimize_constants_x10	0.0357 ± 0.0093 s	0.0353 ± 0.0083 s	1.01
utils/randomly_rotate_tree_x10	5.21 ± 0.58 μs	5.27 ± 0.6 μs	0.988
time_to_load	1.83 ± 0.015 s	1.83 ± 0.039 s	1

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).

[coveralls]

Pull Request Test Coverage Report for Build 12227652648

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 95.222%

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Totals
Change from base Build 12223920533:	0.0%
Covered Lines:	3129
Relevant Lines:	3286

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💛 - Coveralls

[rafaelcuperman]

Thank you very much for this. Works like a charm!