feat(sql): support FETCH row limits

[osipovartem]

Summary

• plan ANSI FETCH FIRST|NEXT <count> ROWS ONLY through DataFusion's existing limit expression path
• combine OFFSET ... ROWS and FETCH into one logical Limit
• support the standard omitted-quantity default of one row
• apply FETCH consistently to SELECT and set-operation queries
• retain explicit errors for unsupported PERCENT and WITH TIES options

Performance

FETCH produces the same logical and physical limit plans as LIMIT. ORDER BY ... FETCH remains eligible for DataFusion's bounded Top-K optimization. The implementation adds no per-row conversion or custom execution operator.

Validation

• cargo +1.95.0 test -p datafusion-sql --test sql_integration (604 passed)
• targeted FETCH planner tests (8 passed)
• targeted SQLLogicTest record errors.slt:78 passed
• cargo +1.95.0 clippy -p datafusion-sql --all-targets -- -D warnings
• cargo +1.95.0 fmt --all -- --check
• git diff --check

The complete fork-specific errors.slt currently has two unrelated pre-existing failures (CAST(c1 AS INT) and a constant-folded division-by-zero case); the changed FETCH record passes when selected directly.