debugger: load 'ipdb' if present

[myhro]

Transparently chooses between the IPython-enhanced ipdb or the standard pdb.

To me, personally, the tab-completion alone is already a killer-feature when debugging locals() variables.

What do you think of adding this option?

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📚 Documentation preview 📚: https://datasette--2342.org.readthedocs.build/en/2342/