Additional control over test order

I have been having a conversion via email about a desired feature. The requester has a very specific test setup where some things must run in a specific order, with other tests running parallel between them.

Currently they use the following yaml file to specify the run order when using prove.

# The wilrcards below ARE NOT regexes, they are globs and
# specific to TAP::Parser::Scheduler. The only possibilities are:
#    ** is any number of characters, including /, within a pathname
#    * is zero or more characters within a filename/directory name
#    ? is exactly one character within a filename/directory name
#    {foo,bar,baz} is any of foo, bar or baz.
#    \ is an escape character
seq:
  - seq:
    - par:
      - t/*
      - xt/{0,1,2,3}*
  - seq:
    - xt/40-dbsetup.t
    - par:
      - xt/40-database.t
      - xt/41-coaload.t
      - xt/45*.t
      - xt/47*.t
      - xt/48*.t
  - seq:
    - par:
      - xt/{43,44,5,7}*.t
      - xt/6{1,2,3,7,8,9}*.t
      - seq:
        - xt/60-startlsmb.t
        - seq:
          - par:
            - xt/6{5,6}*.t
        - seq: **.feature
      - xt/*.pg
  - seq: xt/89-dropdb.t

Achieving this behavior requires 2 things:

1. A custom Test2::Harness::Finder subclass
2. Custom behavior for Test2::Harness::Runner::State::advance_tasks()

I think a new plugin RulesYAML should be added, it can replace the default finder simply enough. Currently there is no way to specify a custom State subclass, but that functionality should not be difficult.

https://metacpan.org/pod/TAP::Parser::Scheduler has a description of the rules used when parsing the yaml file.

Start with Test2::Harness::Finder, Test2::Harness::Runner::State::advance_tasks(), and the TAP::Parser::Scheduler rules linked in the issue. Trace how prove selects and advances tasks, then determine how a RulesYAML plugin and configurable State subclass should support sequential and parallel groups; done means the YAML-described ordering works through the harness.