FilterExec TreeRender format missing fetch display

[zhuqi-lucas]

Description

When FilterExec has a fetch value (from limit pushdown), the TreeRender display format does not include it in the output, while Default/Verbose formats correctly show fetch=N.

This means EXPLAIN FORMAT TREE output is incomplete — the limit information is silently dropped from the FilterExec node.

Steps to Reproduce

CREATE TABLE t1 (a INT) AS VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);

-- Default format shows fetch:
EXPLAIN SELECT a FROM t1 WHERE a > 3 LIMIT 5;
-- FilterExec: a@0 > 3, fetch=5   ✅

-- Tree format does NOT show fetch:
EXPLAIN FORMAT TREE SELECT a FROM t1 WHERE a > 3 LIMIT 5;
-- predicate: a > 3               ❌ (missing fetch=5)

Root Cause

In FilterExec::fmt_as, the TreeRender branch only outputs the predicate:

DisplayFormatType::TreeRender => {
    write!(f, "predicate={}", fmt_sql(self.predicate.as_ref()))
}

While Default/Verbose correctly includes fetch:

write!(f, "FilterExec: {}{}{}", self.predicate, display_projections, fetch)