KNN search accepts negative `k`

[PavelShilin89]

Bug Description:

KNN search accepts negative k values without validation and returns all documents instead of throwing an error.
MRE

CREATE TABLE test (vec FLOAT_VECTOR KNN_TYPE='hnsw' KNN_DIMS='2' HNSW_SIMILARITY='l2');
INSERT INTO test VALUES (1,(1,2)), (2,(3,4));
SELECT COUNT(*) FROM test WHERE KNN(vec, -1, (0,0));

Expected behavior
Should return an error, for example:

ERROR: k parameter must be positive 

Manticore Search Version:

Manticore 13.11.7 bf5b72e3f@25092618 dev (columnar 8.0.6 9a3b45b@25092117) (secondary 8.0.6 9a3b45b@25092117) (knn 8.0.6 9a3b45b@25092117) (embeddings 1.0.1)

Operating System Version:

Ubuntu 24.04.3 LTS

Have you tried the latest development version?

Yes

Internal Checklist:

^{To be completed by the assignee. Check off tasks that have been completed or are not applicable.}

• Implementation completed
• Tests developed
• Documentation updated
• Documentation reviewed

[sanikolaev]

Fixed in #3789

Available for testing in docker image ghcr.io/manticoresoftware/manticoresearch:test-kit-issue-3788:

mysql> CREATE TABLE test (vec FLOAT_VECTOR KNN_TYPE='hnsw' KNN_DIMS='2' HNSW_SIMILARITY='l2');
mysql> INSERT INTO test VALUES (1,(1,2)), (2,(3,4));
mysql> SELECT COUNT(*) FROM test WHERE KNN(vec, -1, (0,0));
ERROR 1064 (42000): P01: k parameter must be positive near ')'

# curl 0:9308/search  -d '
{
    "table": "test",
    "knn":
    {
        "field": "vec",
        "query": [0,0],
        "k": -1
    }
}
'
{"error":"k parameter must be positive"}

@glookka please review the PR