fix: Reset event type after empty SSE block

[lux-in-tenebris-lucet]

Summary

• Reset the buffered event type whenever a blank line ends an SSE block.
• Add dependency-free Node tests covering named events and the regression.

Problem

The parser currently resets its event type only when the completed block contains data.

For this valid event stream:

event: custom

data: hello

the empty custom block leaves its event type buffered. The following hello event is therefore sent to the custom listener instead of the default message listener.

The SSE parsing algorithm requires the event type buffer to be cleared when a block is dispatched, including when the block contains no data.

User impact

Applications using this stream pattern can silently miss messages because the expected message listener is never called. The data may instead be delivered to an unrelated custom-event listener, potentially causing incorrect application behavior.

This is an uncommon stream shape, but it is valid SSE and should be parsed correctly.

Fix

Move the parser-state reset outside the data check so that every blank-line block boundary clears the buffered data and event type.

Testing

• Added a control test for a normal named event.
• Added a regression test for an empty named block followed by a default message.
• Ran npm test: 2 tests passed.

Related to #14 by adding initial automated parser coverage.