Add PyObject.to_int() method returning i64

[nelhage]

Add the py-to-int primitive that extracts a Python integer as i64, complementing the existing from_int method for bidirectional conversion.

Implemented using Claude Code, but reviewed by me before submission. I would find this useful for some current work, where I end up moving between the Python domain and the egglog domain fairly heavily.

[codspeed-hq]

CodSpeed Performance Report

Merging #394 will not alter performance

_{Comparing nelhage:claude/implement-pyobject-to-int-NUp85 (35ea382) with main (6a892ec)}

Summary

✅ 14 untouched

[saulshanabrook]

Thank you! Could you add a little test for this in test_high_level?

Yeah the current set of primitives with py objects are rather arbitrary, would be good to fill them out more.

[nelhage]

Done! Looks like the test failures are infra issues, at a glance.