Fix overflow in timeout logic

Also use steady clock consistently.

Prior to this change, the test would fail under ASAN:

bazel test --config=asan --test_output=errors //sdk/test/metrics:meter_provider_sdk_test
INFO: Analyzed target //sdk/test/metrics:meter_provider_sdk_test (0 packages loaded, 0 targets configured).
FAIL: //sdk/test/metrics:meter_provider_sdk_test (see /private/var/tmp/_bazel_punya/e3bd968ba61238cdeb1a5537fc3dbf7d/execroot/_main/bazel-out/darwin_arm64-fastbuild-asan/testlogs/sdk/test/metrics/meter_provider_sdk_test/test.log)
INFO: From Testing //sdk/test/metrics:meter_provider_sdk_test:
==================== Test output for //sdk/test/metrics:meter_provider_sdk_test:
Running main() from gmock_main.cc
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from MeterProvider
[ RUN      ] MeterProvider.GetMeter
[Warning] File: sdk/src/metrics/meter_provider.cc:65 [MeterProvider::GetMeter] Library name is empty.
[Warning] File: sdk/src/metrics/meter_provider.cc:65 [MeterProvider::GetMeter] Library name is empty.
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__chrono/duration.h:102:59: runtime error: signed integer overflow: 9221646818050376183 * 1000 cannot be represented in type '_Ct' (aka 'long long')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__chrono/duration.h:102:59 in 
================================================================================
INFO: Found 1 test target...
Target //sdk/test/metrics:meter_provider_sdk_test up-to-date:
  bazel-bin/sdk/test/metrics/meter_provider_sdk_test
INFO: Elapsed time: 2.251s, Critical Path: 2.13s
INFO: 5 processes: 5 darwin-sandbox.
INFO: Build completed, 1 test FAILED, 5 total actions
//sdk/test/metrics:meter_provider_sdk_test                               FAILED in 0.6s
  /private/var/tmp/_bazel_punya/e3bd968ba61238cdeb1a5537fc3dbf7d/execroot/_main/bazel-out/darwin_arm64-fastbuild-asan/testlogs/sdk/test/metrics/meter_provider_sdk_test/test.log

Executed 1 out of 1 test: 1 fails locally.

sdk/src/metrics/meter_context.cc

@@ -168,46 +168,36 @@ bool MeterContext::ForceFlush(std::chrono::microseconds timeout) noexcept
   bool result = true;
   // Simultaneous flush not allowed.
   const std::lock_guard<opentelemetry::common::SpinLockMutex> locked(forceflush_lock_);
-  // Convert to nanos to prevent overflow
-  auto timeout_ns = (std::chrono::nanoseconds::max)();
-  if (std::chrono::duration_cast<std::chrono::microseconds>(timeout_ns) > timeout)
-  {
-    timeout_ns = std::chrono::duration_cast<std::chrono::nanoseconds>(timeout);
-  }
-
-  auto current_time = std::chrono::system_clock::now();
-  std::chrono::system_clock::time_point expire_time;
-  auto overflow_checker = (std::chrono::system_clock::time_point::max)();
 
-  // check if the expected expire time doesn't overflow.
-  if (overflow_checker - current_time > timeout_ns)
+  auto time_remaining = std::chrono::steady_clock::duration::max();
+  if (std::chrono::duration_cast<std::chrono::microseconds>(time_remaining) > timeout)
   {
-    expire_time =
-        current_time + std::chrono::duration_cast<std::chrono::system_clock::duration>(timeout_ns);
+    time_remaining = timeout;
   }
-  else
+
+  auto current_time = std::chrono::steady_clock::now();
+  auto expire_time  = std::chrono::steady_clock::time_point::max();
+  if (expire_time - current_time > time_remaining)
   {
-    // overflow happens, reset expire time to max.
-    expire_time = overflow_checker;
+    expire_time = current_time + time_remaining;
   }
 
   for (auto &collector : collectors_)
   {
     if (!std::static_pointer_cast<MetricCollector>(collector)->ForceFlush(
-            std::chrono::duration_cast<std::chrono::microseconds>(timeout_ns)))
+            std::chrono::duration_cast<std::chrono::microseconds>(time_remaining)))
     {
       result = false;
     }
 
-    current_time = std::chrono::system_clock::now();
-
+    current_time = std::chrono::steady_clock::now();
     if (expire_time >= current_time)
     {
-      timeout_ns = std::chrono::duration_cast<std::chrono::nanoseconds>(expire_time - current_time);
+      time_remaining = expire_time - current_time;
     }
     else
     {
-      timeout_ns = std::chrono::nanoseconds::zero();
+      time_remaining = std::chrono::steady_clock::duration::zero();
     }
   }
   if (!result)