feat(sdk): add 32-bit platform support using portable-atomic

Replace std::sync::atomic::{AtomicI64, AtomicU64} with portable-atomic equivalents in the metrics module. This enables compilation on 32-bit ARM platforms (armv5te, armv7) which lack native 64-bit atomics.

The portable-atomic crate uses native atomics on 64-bit platforms (zero overhead) and provides a software fallback on 32-bit platforms.

Author: neeme-praks-sympower

opentelemetry-sdk/Cargo.toml

@@ -25,6 +25,7 @@ url = { workspace = true, optional = true }
 tokio = { workspace = true, default-features = false, optional = true }
 tokio-stream = { workspace = true, optional = true }
 http = { workspace = true, optional = true }
+portable-atomic = { version = "1", default-features = false, features = ["fallback"] }
 
 [package.metadata.docs.rs]
 all-features = true

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

@@ -10,7 +10,8 @@ use std::cmp::min;
 use std::collections::{HashMap, HashSet};
 use std::mem::swap;
 use std::ops::{Add, AddAssign, DerefMut, Sub};
-use std::sync::atomic::{AtomicBool, AtomicI64, AtomicU64, AtomicUsize, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+use portable_atomic::{AtomicI64, AtomicU64};
 use std::sync::{Arc, OnceLock, RwLock};
 
 pub(crate) use aggregate::{AggregateBuilder, AggregateFns, ComputeAggregation, Measure};