feat(lenses): the commit-truth lens, repo-facts, as Gate 4

Every claim in every commit message, and in the documentation the range
adds or changes, proven or gone. The lens's block kinds are text, doc and
slot: a message unit is keyed on its text, the base and the code up to its
commit (MessageDeps); a documentation unit on its file, its normalised
text, the base and the code of the whole range (DocKeyParts); a diffstat on
its text alone; whole:order and whole:absent are asked in slot passes of
its own, never stored. A documentation file's diff header and a part the
commit writes nothing in are a mechanical n/a. Budgets 60/40 for a text or
doc block, 50/35 for a slot; one read. Gate 4, after the proofs, so the
messages and documents are read once the code they describe has settled;
the owner's gate is 5.

The goldens that follow from the lens table are derived by
tests/Goldens/derive.py, which asserts that the recorded table still
reproduces the recorded entries before it writes.

Proven, with the opt-in commit after this one: the suite (26 passed); a dry
run of a scratch range (2 commits, a README with sections) by the previous
binary and this one with the three static lenses on and the rest off, 25
prompts and 4 system files byte for byte; with repo-facts on as well,
those files unchanged and 10 passes and 1 system file added.
The lens's firing proof in this pipeline is owed (the owner's go).

implementations/Crafter.Review-Run.cpp

@@ -498,8 +498,7 @@ namespace Crafter::Review::Run {
         }
         const std::vector<std::string> exclude = Strings(cfg.at("functional").at("exclude"));
         notReviewed = Plan::NotReviewed(units, lines, running, exclude);
-        log(std::format("inventory: {} units ({}); {} units no lens that runs reads (text, documentation, the units of a lens the config turns off)", units.size(), Dyn::RelPath(invPath.string(), repo.string()),
-                        notReviewed.size()));
+        log(std::format("inventory: {} units ({}); {} units no lens that runs reads", units.size(), Dyn::RelPath(invPath.string(), repo.string()), notReviewed.size()));
         if (a.units) {
             std::set<std::string> known;
             for (const Json& u : units) known.insert(Dyn::Str(u.at("id")));