Scope capacities for build-tool scopes, patterns and serial queues

scopes.capacities only accepted letters, digits, - and _ in its keys, so the scope names Bazel (//lib/core), Pants (lib/util) and Turborepo (@acme/web) report could not be given a capacity. A capacity key now accepts any scope name you send through the scopes API.

A key can also be a glob pattern, such as //lib/** or @acme/*. Every scope it matches gets its own capacity, so a whole family of lanes can be capped without listing each one. A key naming the scope exactly wins over a pattern, the lowest capacity applies when several patterns match, and default_capacity still covers every scope no key matches.

Scope capacities also work in a serial queue, the default mode, which used to refuse them. A serial queue still runs up to max_parallel_checks speculative checks, so you can keep an expensive scope, such as an end-to-end suite, to one check at a time while the rest of the queue uses the other slots. A pull request whose scope is full waits for a slot there while later pull requests that fit go ahead, and it is still tested on top of everything that merges before it.