Fixed #500

Currently, source (input-less) Dora nodes close their event stream immediately after startup, making them unable to receive an ‎⁠Event::Stop⁠ signal (such as from Ctrl+C or ‎⁠dora stop⁠). This prevents graceful shutdown.

Solution:

A new optional node configuration field, ‎⁠wait_for_stop: bool⁠, is introduced to control event stream behavior after all inputs are closed:

• ‎⁠wait_for_stop: false⁠: The event stream ends when all inputs are closed (default for nodes with inputs; unchanged).
• wait_for_stop: true⁠: The event stream remains open until an explicit ‎⁠Event::Stop⁠ signal is received (default for source nodes with no inputs).

Users can override the default by setting this option explicitly in the dataflow YAML file.

Key Changes:

1. dora-message⁠:
   • Added ‎⁠wait_for_stop: Option<bool>⁠ to ‎⁠descriptor::Node⁠ for YAML parsing.
   • Added ‎⁠wait_for_stop: bool⁠ to ‎⁠descriptor::ResolvedNode⁠ to store the resolved value.
2. dora-core⁠:
   • Updated ‎⁠descriptor::resolve_aliases_and_set_defaults⁠ to compute the final ‎⁠ResolvedNode.wait_for_stop⁠ value based on inputs and YAML settings. Fixed related ownership bug.
3. cora-daemon⁠:
   • Updated node spawning (‎⁠spawn::spawn_node⁠) to pass ‎⁠ResolvedNode.wait_for_stop⁠ to the node communication listener (‎⁠node_communication::spawn_listener_loop⁠ and implementation).
   • Modified listener logic (‎⁠node_communication::Listener⁠) to check the ‎⁠wait_for_stop⁠ flag when deciding whether to send ‎⁠AllInputsClosed⁠ or end the event stream. The event stream now only ends naturally if ‎⁠wait_for_stop⁠ is ‎⁠false⁠.
   • Ensured all nodes’ event streams can be stopped by ‎⁠Event::Stop⁠, regardless of ‎⁠wait_for_stop⁠.
4. Updated ‎⁠dora-schema.json⁠ to include the ‎⁠wait_for_stop⁠ field.

Impact:

• Source nodes now stay running by default and can respond to stop signals as expected.
• Users who want source nodes to exit immediately can set ‎⁠wait_for_stop: false⁠.
• Nodes with inputs retain their default (exit when inputs close), but can be set to wait for stop if desired.
• Fixed a bug in config resolution due to ownership issues.

Todos:

• Update core documentation (‎⁠libraries/core/README.md⁠) to explain the new config and defaults.
• Update Node API docs (Rust, Python, C, C++) about event stream lifecycle.

Todo Test:

• Source node default (waits for Stop).
• Source node with ‎⁠wait_for_stop: false⁠ (exits immediately).
• Node with inputs default (ends when inputs close).
• Node with inputs and ‎⁠wait_for_stop: true⁠ (waits for Stop).
• Stopping with Ctrl+C and ‎⁠dora stop⁠.