Add Elixir API for set_busy_timeout and cancel

- Add NIF stubs: set_busy_timeout/2, cancel/1
- Add public wrappers: Sqlite3.set_busy_timeout/2, Sqlite3.cancel/1
- cancel/1 includes nil guard (matches close/1 and interrupt/1 convention)
- Fix bind_parameter_count/1 typespec: integer -> non_neg_integer() | {:error, reason()}
- Fix bind_parameter_index/2 typespec: integer -> non_neg_integer() | {:error, reason()}

The typespec fixes address pre-existing dialyzer warnings - both NIFs can return
{:error, :invalid_statement} when statement->statement is NULL.

Author: mjc

lib/exqlite/sqlite3.ex

@@ -100,6 +100,29 @@ defmodule Exqlite.Sqlite3 do
   def interrupt(nil), do: :ok
   def interrupt(conn), do: Sqlite3NIF.interrupt(conn)
 
+  @doc """
+  Set the busy timeout in milliseconds without destroying the custom busy handler.
+
+  Unlike `PRAGMA busy_timeout` (which internally calls `sqlite3_busy_timeout()`
+  and replaces any custom handler), this function only updates the timeout value
+  that the custom busy handler reads. This preserves the ability to cancel
+  busy waits via `cancel/1`.
+  """
+  @spec set_busy_timeout(db(), integer()) :: :ok | {:error, reason()}
+  def set_busy_timeout(conn, timeout_ms),
+    do: Sqlite3NIF.set_busy_timeout(conn, timeout_ms)
+
+  @doc """
+  Cancel a running query: wake any busy handler sleep and interrupt VDBE execution.
+
+  This is a superset of `interrupt/1` — it sets a cancel flag, signals the
+  condvar to wake any busy handler sleep, AND calls `sqlite3_interrupt()`.
+  After a cancel, the connection can be reused normally.
+  """
+  @spec cancel(db() | nil) :: :ok | {:error, reason()}
+  def cancel(nil), do: :ok
+  def cancel(conn), do: Sqlite3NIF.cancel(conn)
+
   @doc """
   Executes an sql script. Multiple stanzas can be passed at once.
   """
@@ -136,7 +159,7 @@ defmodule Exqlite.Sqlite3 do
       2
 
   """
-  @spec bind_parameter_count(statement) :: non_neg_integer | {:error, atom()}
+  @spec bind_parameter_count(statement) :: non_neg_integer() | {:error, reason()}
   def bind_parameter_count(stmt), do: Sqlite3NIF.bind_parameter_count(stmt)
 
   @type bind_value ::

lib/exqlite/sqlite3_nif.ex

@@ -26,6 +26,12 @@ defmodule Exqlite.Sqlite3NIF do
   @spec interrupt(db()) :: :ok | {:error, reason()}
   def interrupt(_conn), do: :erlang.nif_error(:not_loaded)
 
+  @spec set_busy_timeout(db(), integer()) :: :ok | {:error, reason()}
+  def set_busy_timeout(_conn, _timeout_ms), do: :erlang.nif_error(:not_loaded)
+
+  @spec cancel(db()) :: :ok | {:error, reason()}
+  def cancel(_conn), do: :erlang.nif_error(:not_loaded)
+
   @spec execute(db(), String.t()) :: :ok | {:error, reason()}
   def execute(_conn, _sql), do: :erlang.nif_error(:not_loaded)
 
@@ -69,10 +75,11 @@ defmodule Exqlite.Sqlite3NIF do
   @spec set_log_hook(pid()) :: :ok | {:error, reason()}
   def set_log_hook(_pid), do: :erlang.nif_error(:not_loaded)
 
-  @spec bind_parameter_count(statement) :: integer
+  @spec bind_parameter_count(statement) :: non_neg_integer() | {:error, reason()}
   def bind_parameter_count(_stmt), do: :erlang.nif_error(:not_loaded)
 
-  @spec bind_parameter_index(statement, String.t()) :: integer
+  @spec bind_parameter_index(statement, String.t()) ::
+          non_neg_integer() | {:error, reason()}
   def bind_parameter_index(_stmt, _name), do: :erlang.nif_error(:not_loaded)
 
   @spec bind_text(statement, non_neg_integer, String.t()) :: integer()