Count the build's allocations on generated projects in the benchmarks

Why:
    The benchmarks compile runtime and Belt files one at a time, whose
    dependency graphs are small, and build tests/tests, whose modules use
    a few small modules. Costs that grow with how many modules a build has
    or loads barely show: a change that avoids copying the signatures of
    large dependencies that a module hardly reads moved them by 0.4%, and
    opening the map of a namespaced package, which is quadratic in its
    modules per build, doesn't run at all.

With `--project`, `measure` now also builds two projects that the script
generates, clean and after an edit, on one worker domain and counting
allocated words like tests/tests:

- WideDeps: 240 modules that each use one or two values of four modules
  with 600 types and 1,200 values each. The edit adds a value to one of
  them, which compiles its users again.
- Namespace: a package with `"namespace": true` and 1,000 one-line
  modules. The edit changes a module that nothing uses.

Their counts are larger than all the others together, so the report adds
them up on a line of their own, `Generated projects`, and `In total`
covers the other benchmarks as before. Each has its row and threshold like
any other benchmark. Every module of a project build loads the runtime's
interfaces, so the inputs of the generated projects and of tests/tests now
include a hash of the runtime sources: a pull request that changes the
runtime marks them as inputs changed rather than as regressions.

Locally, the signature copy pull requests take WideDeps clean from 505M
to 333M words and its edit from 232M to 146M, and building the namespace
map on demand takes Namespace clean from 611M to 203M; the other
benchmarks' counts are unchanged. The builds of tests/tests now share
countBuild and editModule with the generated projects.

Signed-off-by: Jono Prest <jjprest@gmail.com>

Author: JonoPrest

.github/workflows/ci.yml

@@ -455,7 +455,8 @@ jobs:
           # to 0.2%. The runtime and Belt are built there too, since the
           # replayed builds would otherwise write interfaces that don't
           # match those of the files they don't replay yet. Both build the
-          # base's tests/tests, which the base's compiler builds already.
+          # base's tests/tests, which the base's compiler builds already,
+          # and the generated projects of this checkout's script.
           measure() {
             sudo mkdir -p /bench
             sudo mount --bind "$1" /bench

changes/generated-project-benchmarks.internal.md

@@ -0,0 +1 @@
+- Count the words the build allocates on generated projects in the CI benchmarks: many modules using little of a few large dependencies, and a namespaced package of 1,000 modules.