EXP: use py check_signals() to catch CTRL-C

[ctb]

Fixes #40.

Per #40 (comment),

so there's a much simpler way via pyo3! I just enabled this in the directsketch plugin:

1. Pass in py /_py from lib to main function

• https://github.com/sourmash-bio/sourmash_plugin_directsketch/blob/main/src/lib.rs#L86-L91
• https://github.com/sourmash-bio/sourmash_plugin_directsketch/blob/main/src/directsketch.rs#L603

2. Include use pyo3::prelude::*; and call py.check_signals in main function:

• https://github.com/sourmash-bio/sourmash_plugin_directsketch/blob/main/src/directsketch.rs#L669

Related issues:

• Closes WIP: add Ctrl-C interrupt #253
• Closes WIP: improve/extend thread management and ctrl-c #276

[ctb]

Main problem right now - can't use py.check_signals() inside a closure 🤔