fix: abort waitFor server_interactive tests promptly on file worker fatal error

[nomeata]

This PR makes the test-only waitForMessage helper abort promptly
when the Lean language server reports a fatalError, instead of
blocking until the outer test framework's timeout kills the process.

waitForMessage is used to implement the waitFor directive in
tests/server_interactive tests: it reads server messages in a loop
and returns when it sees a textDocument/publishDiagnostics
notification containing a given message. It has no pending request,
so the watchdog's responseError (which already terminates
collectDiagnostics and waitForILeans on a fatalError) doesn't
help here, and it would silently discard $/lean/fileProgress
notifications. When the file worker crashes or its header processing
fails fatally (e.g. an unresolved import), the awaited diagnostic
will never be emitted -- so waitForMessage would block indefinitely
and report nothing useful, which made several CI failures of
server_interactive tests look like generic 1500s timeouts. With this
change, waitForMessage also reacts to $/lean/fileProgress with
fatalError kind and throws a descriptive error.

The detection is scoped to waitForMessage only, not the underlying
Ipc.readMessage, so that other IPC paths (notably
importCompletion.lean, which intentionally elaborates a file with
an incomplete import line and observes the resulting fatalError
fileProgress while still using the alive worker for completion
requests) keep working unchanged. As part of this PR, waitForMessage
has been moved out of Lean.Lsp.Ipc and into
Lean.Server.Test.Runner next to its sole caller processWaitFor,
since it is a test-driver helper rather than a general-purpose IPC
primitive (it discards all unrelated messages, which would be unsafe
outside of a test driver).

To exercise the new behavior, tests/server_interactive/run_test.sh
now sources <file>.init.sh and uses check_exit_is "${TEST_EXIT:-0}",
matching the convention in tests/compile/. The new
worker_crash.lean test forces the file worker to die via
IO.Process.forceExit 9 from inside an elab command and then
issues a waitFor directive that can never be satisfied;
TEST_EXIT=1 and .out.expected capture the abort path. Without
this PR the test would sit at the framework timeout; with this PR it
returns in well under a second.

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase f52a18a9472f40a864a78d3c8f8cf202751f576b --onto 2229b077d6ebd2ff42d665fe1c32501df8915dff. You can force Mathlib CI using the force-mathlib-ci label. (2026-05-11 20:12:10)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase f52a18a9472f40a864a78d3c8f8cf202751f576b --onto c04a83a2e5d5718032819f2d124f2c949fab292f. You can force Mathlib CI using the force-mathlib-ci label. (2026-05-12 14:00:58)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase f52a18a9472f40a864a78d3c8f8cf202751f576b --onto a71f158f7bd96ff9ea846f7ff4cc658de3c8b0f9. You can force reference manual CI using the force-manual-ci label. (2026-05-11 20:12:12)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase f52a18a9472f40a864a78d3c8f8cf202751f576b --onto c04a83a2e5d5718032819f2d124f2c949fab292f. You can force reference manual CI using the force-manual-ci label. (2026-05-12 14:01:00)