Read counter not reported in PageCacheWrapper

Description:

The Read counter in bf-tree's internal metrics is only incremented within the BfTree::read() method. However, the PageCacheWrapper in the benchmark/ subdirectory implements its point-read logic using db.scan_with_count(key, 1, ...).

Because this approach bypasses the BfTree::read() method, point-read operations are not tracked in the Read counter, leading to a reported value of "Read": 0 in benchmark JSON results, even when throughput is high.

Proposed Fix:

Manually invoke the counter!(Read) macro within the read() implementation of the PageCacheWrapper to ensure these operations are consistently tracked alongside other engines.

Example Fix:

// benchmark/src/wrappers/page_cache_wrapper.rs

fn read(&self, key: &[u8], value: &mut [u8]) -> usize {
    bf_tree::counter!(Read); // Ensure point-reads via scan are recorded
    let mut iter = self.db.scan_with_count(key, 1, ScanReturnField::Value)
        .expect("Failed to create scan iterator");
    // ...
}

Open benchmark/src/wrappers/page_cache_wrapper.rs and inspect PageCacheWrapper::read(), which performs point reads through scan_with_count. Add the Read counter invocation described in the issue, then run the relevant benchmark and confirm the JSON results report a nonzero Read count.