Use conda-build instead of conda-mambabuild

[bdice]

This changes from conda mambabuild to conda build. Conda now uses the mamba solver so no performance regressions are expected.

This is a temporary change as we plan to migrate to rattler-build in the near future. However, this is needed sooner to drop boa and unblock Python 3.13 migrations.

xref: rapidsai/build-planning#149

[jameslamb]

Looks good! I'll note here (haven't in the other reviews), I've also been spot-checking that sccache is still working and yeah, looks fine.

Compile requests                    186
Compile requests executed           186
Cache hits                          186
Cache hits (c [gcc])                 21
Cache hits (c++ [gcc])              165

(build link)

[jameslamb]

/merge