Add runnable `.sql` examples and regression tests for the built-in graph algorithms

[Leomrlin]

What & why

GeaFlow ships 19 built-in graph algorithms (PageRank, SSSP, WCC, Louvain, LPA,
KCore, TriangleCount, JaccardSimilarity, …), but the geaflow-dsl-runtime
regression suite only covers some of them. Filling in end-to-end
CALL ... YIELD tests for the rest guards against future refactors quietly
breaking an algorithm. Great if you want to understand what graph algorithms
actually compute.

GeaFlow 有 19 个内置图算法,但回归测试只覆盖了一部分。给其余算法补端到端的
CALL ... YIELD 测试,能防止后续重构悄悄改坏算法。想真正搞懂"图算法到底算了什么"的同学,这题很合适。

The task

Pick a few algorithms that have no tests (or thin coverage) and add .sql
queries + .txt expected outputs.

挑几个尚无测试或覆盖薄弱的算法,补 .sql 查询 + .txt 期望输出。

Where to look

1. Test graph definition: geaflow-dsl-runtime/src/test/resources/modern_graph.sql.
2. Query template: existing query/gql_algorithm_001.sql
   (CALL SSSP(1) YIELD (vid, distance) style); expected output at expect/gql_algorithm_001.txt.
3. Test entry point: geaflow-dsl-runtime/.../runtime/query/GQLAlgorithmTest.java.

Done when

• At least one .sql/.txt pair added per algorithm you claim
• Expected outputs are verified by hand, not copied from program output
• mvn test -Dtest=GQLAlgorithmTest passes
• The PR briefly explains why each expected result is correct on the test graph

[wipheg]

hi @Leomrlin , i'd like to work on this issue. could you assign this to me?