Optimize StrictMetricsEvaluator reference binding and add benchmarks

[SURYAS1306]

Summary

This PR implements the filtering hot-path optimization and benchmark infrastructure proposed in #690.

• Replace RETURN_IF_NOT_REFERENCE with BIND_REFERENCE_OR_RETURN in StrictMetricsEvaluator so predicate handlers reuse the dynamic_cast result instead of calling expr->reference() (which bumps shared_ptr refcounts via shared_from_this()).
• Add an off-by-default ICEBERG_BUILD_BENCHMARKS CMake option that fetches Google Benchmark (v1.9.1) and builds strict_metrics_evaluator_bench.

Motivation

StrictMetricsEvaluator runs once per data file during scan planning. The previous macro discarded a successful dynamic_cast and then re-fetched the same reference through a virtual call + atomic refcount operation on every predicate handler (14+ predicate types).

Benchmark results (Release, Apple Clang 17, macOS)

Micro-benchmark model of the predicate binding hot path:

Benchmark	Before	After	Gain
Single predicate	21.0 ns	12.4 ns	1.69×
14 preds / file	206 ns	113 ns	1.82×
20 preds / file	294 ns	160 ns	1.84×

End-to-end StrictMetricsEvaluator::Evaluate benchmark (with binding + evaluation):

Predicates	Time
1	~137 ns
14	~2.3 µs
20	~3.3 µs

Test plan

• expression_test --gtest_filter='StrictMetrics*' (42 tests pass)
• Build with -DICEBERG_BUILD_BENCHMARKS=ON
• Run ./benchmark/strict_metrics_evaluator_bench

Closes #690

[Copilot]

Pull request overview

This PR optimizes StrictMetricsEvaluator’s predicate reference binding by reusing the dynamic_cast result (avoiding repeated shared_from_this() refcount bumps), and adds an off-by-default benchmark build option plus an initial Google Benchmark target to measure the filtering hot path.

Changes:

• Replace the RETURN_IF_NOT_REFERENCE pattern with BIND_REFERENCE_OR_RETURN so each predicate handler reuses the already-casted BoundReference*.
• Add ICEBERG_BUILD_BENCHMARKS CMake option and a src/iceberg/benchmark/ subdirectory that fetches Google Benchmark and builds strict_metrics_evaluator_bench.
• Enable ICEBERG_BUILD_BENCHMARKS=ON in the cpp-linter workflow build step to ensure the benchmark target stays buildable in CI.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/iceberg/expression/strict_metrics_evaluator.cc	Hot-path optimization: reuse dynamic_cast result instead of calling reference() repeatedly.
CMakeLists.txt	Add ICEBERG_BUILD_BENCHMARKS option (default OFF).
src/iceberg/CMakeLists.txt	Wire benchmark subdir behind ICEBERG_BUILD_BENCHMARKS.
src/iceberg/benchmark/CMakeLists.txt	Fetch Google Benchmark and define the benchmark executable target.
src/iceberg/benchmark/strict_metrics_evaluator_bench.cc	Add initial micro-benchmark for StrictMetricsEvaluator::Evaluate.
.github/workflows/cpp-linter.yml	Turn on benchmarks during CI build to catch build regressions.

[github-actions]

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