Compatibility with latest Copier

[doshitan]

The latest official release of Copier (at time of writing) is v9.4.1 (released Oct 2024). This project currently pins to particular commit of Copier slightly beyond v9.4.1 due to some useful unreleased improvements. But we can't update further than that commit due to breaking changes in Copier. Eventually a new proper release will be tagged and we should update to it.

Dynamic file structures

This is the breaking change in Copier: copier-org/copier@557c0d6

See 7d266fc for more details. But we mainly just need pick another place to override for src_exclude support. If we choose to move forward with navapbc/template-infra#818, we could likely drop the src_exclude stuff altogether, which simplifies the work here.

This may enable use to re-consider how we treat template-infra/the InfraTemplate class. See navapbc/template-infra#857

Template Composition

A little different, and could be separate, but by the time we get to addressing the above, another change may be available that we'll want to consider: copier-org/copier#1880

Instead of needing to build custom support in the CLI for sharing the base and app answers.