Call interrupt before close in disconnect to fix deadlock

When DBConnection times out a long-running query, it calls disconnect/2
on the connection process. Previously, disconnect only called Sqlite3.close(),
which blocks on conn->mutex held by the still-running dirty NIF — deadlocking
the pool permanently.

Now disconnect calls Sqlite3.interrupt(db) first, which sets a flag checked
at every VDBE loop iteration (OP_Next, OP_Prev, etc.). The running query
aborts with SQLITE_INTERRUPT, releases the mutex, and close() proceeds.

This is safe because PR #342 (v0.35.0) added interrupt_mutex to the NIF
layer, which prevents a use-after-free race between interrupt() and close().
The interrupt_mutex ensures interrupt reads the db pointer atomically even
if close() is freeing it concurrently.

Test results before this change:
  149 tests, 20 pass, 2 fail (pool recovery test deadlocks at 30s timeout)

Test results after this change:
  160 tests, 2 failures
  - 21 of 22 cancellation tests now pass (busy handler test still fails as expected)
  - The integration test "exceeding timeout" fails with a pattern match error
    (expects {:ok, _, _} but gets {:error, "interrupted"} — will be fixed later)

The passing cancellation tests demonstrate that interrupt successfully unblocks
queries stuck in VDBE execution, fixing the primary deadlock issue.

Known limitation: does not fix the case where a query is stuck in SQLite's
busy handler sleep loop (waiting for a lock held by another connection).
That requires a custom busy handler (separate change).

Fixes the primary deadlock described in #192.

Author: mjc

lib/exqlite/connection.ex

@@ -212,6 +212,11 @@ defmodule Exqlite.Connection do
       apply(state.before_disconnect, [err, state])
     end
 
+    # Interrupt any in-flight query so close() doesn't block on conn->mutex.
+    # Without this, a long-running dirty NIF holds the mutex and close() deadlocks.
+    # See: https://github.com/elixir-sqlite/exqlite/issues/192
+    Sqlite3.interrupt(db)
+
     case Sqlite3.close(db) do
       :ok -> :ok
       {:error, reason} -> {:error, %Error{message: to_string(reason)}}