fix(lib): prevent finished_tree assertion failure

**Problem:** When resetting the parser during subtree balancing, an
error is thrown:

```
parser.c:2198: ts_parser_parse: Assertion `self->finished_tree.ptr' failed.
```

**Solution:** Reset `canceled_balancing` to false in
`ts_parser_reset()`.

cli/src/tests/parser_test.rs

@@ -1004,6 +1004,31 @@ fn test_parsing_with_timeout_during_balancing() {
         assert!(tree.is_none());
         assert!(in_balancing);
 
+        // This should not cause an assertion failure.
+        parser.reset();
+        let tree = parser.parse_with_options(
+            &mut |offset, _| {
+                if offset >= code.len() {
+                    &[]
+                } else {
+                    &code.as_bytes()[offset..]
+                }
+            },
+            None,
+            Some(ParseOptions::new().progress_callback(&mut |state| {
+                if state.current_byte_offset() != current_byte_offset {
+                    current_byte_offset = state.current_byte_offset();
+                    false
+                } else {
+                    in_balancing = true;
+                    true
+                }
+            })),
+        );
+
+        assert!(tree.is_none());
+        assert!(in_balancing);
+
         // If we resume parsing (implying we didn't call `parser.reset()`), we should be able to
         // finish parsing the tree, continuing from where we left off.
         let tree = parser

lib/src/parser.c

@@ -2080,6 +2080,7 @@ void ts_parser_reset(TSParser *self) {
   self->accept_count = 0;
   self->has_scanner_error = false;
   self->has_error = false;
+  self->canceled_balancing = false;
   self->parse_options = (TSParseOptions) {0};
   self->parse_state = (TSParseState) {0};
 }