fix(id): name the hanging group in nixos-integration VM test (#1372) - #4913

What

pkgs/id/nix/tests/integration-test.nix ran the entire cli_integration
binary as one server.succeed() with --test-threads=2 --nocapture --format=terse, so a hang produced only timeout reached; test terminating...
with no test name or wait target (#1372, recurrence of #896's acceptance).

This makes the harness legible without changing what is covered:

• Four named groups — fast_unit (49 tests), serve (43), tag (29),
  harness_unit (5) — each run under its own GNU timeout deadline
  (900/2200/400/300 s) instead of one 3600 s globalTimeout.
• The wait target is logged before every group: group name, libtest
  filters, effective deadline, and remaining suite budget.
• --format=pretty replaces --format=terse, so completed tests stream
  into the log and libtest prints test <name> has been running for over 60 seconds for anything still running.
• A 3400 s suite budget clamps each group's deadline to what is left, so a
  hang always fails with a named group inside the budget rather than at the
  driver's globalTimeout = 3600 (which stays as the backstop).
• Every group still runs after a failure, and the run ends with a summary
  naming all failed groups — a failing serve no longer hides tag or
  harness_unit results.
• A coverage guard runs TEST_BIN --list first and proves the group
  filters partition every test exactly once. A new test module that is not in
  GROUPS fails immediately with the uncovered names instead of silently
  being dropped.

Validation (real VM, 2026-11-03)

nix build .#checks.x86_64-linux.nixos-integration on the branch, reusing the
branch's built integrationTestRunner and id binary. The stock build is
currently blocked before the VM by the pre-existing #4850 checkPhase failure,
so only that unrelated id-web checkPhase was skipped; the harness and all
126 tests ran unchanged.

[id-integration] 126 tests in 4 named groups: fast_unit=49, serve=43, tag=29, harness_unit=5
[id-integration] waiting on group 'fast_unit' (...); per-group deadline 900s, 3400s of suite budget left
[id-integration] group 'fast_unit' finished in 7.4s
[id-integration] waiting on group 'serve' (filters: serve_tests::); per-group deadline 2200s, 3384s of suite budget left
test result: FAILED. 40 passed; 3 failed; ... finished in 17.06s
[id-integration] group 'serve' failed or exceeded its 2200s deadline; filters: serve_tests::; continuing
[id-integration] group 'tag' finished in 1.2s
[id-integration] group 'harness_unit' finished in 4.3s
AssertionError: [id-integration] failed groups: serve

The three serve failures are pre-existing and now name themselves:
test_world_join_via_ssh_carries_the_frame_protocol,
test_world_ssh_tunnel_carries_join_via_ssh, and
test_world_module_shared_over_iroh_and_web_presentations, all rooted in the
id binary being built without the ssh feature — filed as #4960. Before
this change that failure arrived as a bare terse log.

A deliberate short-deadline run (same harness, serve deadline 5 s) produced:

[id-integration] waiting on group 'serve' (filters: serve_tests::); per-group deadline 5s, 3392s of suite budget left
AssertionError: [id-integration] group 'serve' failed or exceeded its 5s deadline; filters: serve_tests::

Other checks: nix eval of the check derivation, python3 -m py_compile of
the emitted testScript, nixfmt clean.

Remaining blockers for a green stock check (pre-existing, not this PR)

• id(chain): ChainExt literals in pkgs/id tests missing the #3794 checkpoint field — cargo check --all-targets fails on main #4850 — id-web checkPhase fails on main (ChainExt literals missing the
  id: protocol v1 phase 1 — session header + segment checkpoint event kind (#2036) #3794 checkpoint field).
• id(ci): nixos-integration's id binary lacks the ssh feature, so the SSH world tests fail #4960 — the VM test's id binary is built without ssh, so the SSH world
  tests cannot pass.

This PR is reporting-only; the suite's coverage is unchanged.

Refs #1372. Scope deliberately excludes chasing which test hangs and editing
the integration tests themselves.