Allow empty `ColList` + Bump Rust to 1.80.1

[Centril]

Description of Changes

Fix the bug found in https://github.com/clockworklabs/SpacetimeDB/pull/1585 by allowing ColLists to be empty, as we actually try to use the type as a possibly-empty list in some places (which is why the tests failed in #1585).

Bump Rust to 1.80.1 as this turned out to be required due to compiler bugs on 1.78.

Closes https://github.com/clockworklabs/SpacetimeDB/pull/1585.

API and ABI breaking changes

None

Expected complexity level and risk

2, some unsafe related code affected, but there's less unsafe code now.

Testing

• [x] Tests were extended to test the empty aspect and the new functionality.
• [x] All the ColList proptests were run in miri.