The paths are even weirder inside the build environment.

We're abusing combine to rewrite paths in the coverage data.  combine isn't
intended to be used with only one coverage data file named ".coverage".  So
enable parallel mode so we have only one coverage data file with the naming
scheme "combine" expects.

Maybe this gets us working path rewriting on Windows,

codecov docs say that xml is supported and explicitly call out Python
".coverage" format as unsupported.

https://docs.codecov.io/docs/supported-report-formats

Something fails with "No usable data files" on CI, not sure what

Disable the Eliot test suite in the Nix package build

Emit an Eliot message when spending happens at the lowest level

A ZKAP is now worth 1 MiB instead of 128 KiB

This removes almost all uses of the global value.  All that remains is its use
as a default in case no configuration is given.

Call redeemWithCounter with a Voucher object instead of voucher text

Add counter to database and Python representation