perf(sdk): use ahash for ValueMap HashMaps in metrics hot path

Replace the default SipHash-1-3 hasher with ahash (AES-NI backed) for
the HashMap used in ValueMap::trackers. SipHash's HashDoS resistance is
unnecessary here since ValueMap is pub(crate) and keys are not
attacker-controlled. ahash leverages hardware AES instructions for
significantly faster hashing of Vec<KeyValue> keys.

Refs: #3371

Co-Authored-By: Bryant Biggs <bryantbiggs@gmail.com>

Author: bryantbiggs

opentelemetry-sdk/Cargo.toml

@@ -11,6 +11,7 @@ rust-version = "1.75.0"
 autobenches = false
 
 [dependencies]
+ahash = "0.8"
 opentelemetry = { workspace = true }
 opentelemetry-http = { workspace = true, optional = true }
 futures-channel = { workspace = true }

opentelemetry-sdk/src/metrics/internal/mod.rs

@@ -5,11 +5,12 @@ mod last_value;
 mod precomputed_sum;
 mod sum;
 
+use ahash::AHashMap as HashMap;
 use core::fmt;
 #[cfg(not(target_has_atomic = "64"))]
 use portable_atomic::{AtomicI64, AtomicU64};
 use std::cmp::min;
-use std::collections::{HashMap, HashSet};
+use std::collections::HashSet;
 use std::mem::swap;
 use std::ops::{Add, AddAssign, DerefMut, Sub};
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};