feat(sum): use larger buffer in bsd_sum and sysv_sum

src/uu/sum/BENCHMARKING.md

@@ -13,11 +13,11 @@ cargo build --release --package uu_sum
 and then you can time how it long it takes to checksum the file by running
 
 ```shell
-time ./target/release/sum wikidatawiki-20211001-pages-logging.xml
+time ./target/release/sum wikidatawiki-20251220-pages-logging.xml
 ```
 
 For more systematic measurements that include warm-ups, repetitions and comparisons, [Hyperfine](https://github.com/sharkdp/hyperfine) can be helpful. For example, to compare this implementation to the one provided by your distribution run
 
 ```shell
-hyperfine "./target/release/sum wikidatawiki-20211001-pages-logging.xml" "sum wikidatawiki-20211001-pages-logging.xml"
+hyperfine "./target/release/sum wikidatawiki-20251220-pages-logging.xml" "sum wikidatawiki-20251220-pages-logging.xml"
 ```

src/uu/sum/src/sum.rs

@@ -16,8 +16,11 @@ use uucore::translate;
 
 use uucore::{format_usage, show};
 
+// Fixed to 8 KiB (equivalent to `std::sys::io::DEFAULT_BUF_SIZE` on most targets)
+const DEFAULT_BUF_SIZE: usize = 8 * 1024;
+
 fn bsd_sum(mut reader: impl Read) -> std::io::Result<(usize, u16)> {
-    let mut buf = [0; 4096];
+    let mut buf = [0; DEFAULT_BUF_SIZE];
     let mut bytes_read = 0;
     let mut checksum: u16 = 0;
     loop {
@@ -41,7 +44,7 @@ fn bsd_sum(mut reader: impl Read) -> std::io::Result<(usize, u16)> {
 }
 
 fn sysv_sum(mut reader: impl Read) -> std::io::Result<(usize, u16)> {
-    let mut buf = [0; 4096];
+    let mut buf = [0; DEFAULT_BUF_SIZE];
     let mut bytes_read = 0;
     let mut ret = 0u32;