Upgrade go.opentelemetry.io/otel/sdk to v1.40.0

[yuandrew]

What was changed

Combined #2211, #2210, and #2209 into a single PR

Added a nil check for tests, now that EventuallyWithT runs immediately, instead of after a tick, stretchr/testify#1427

Fixed TestPinnedOverrideInWorkflowOptions test flake. An existing race, but potentially amplified by go 1.24.0 bump, which changed goroutine scheduling behavior. Fixed by retrying ExecuteWorkflow in an Eventually loop until the pinned verison is present.

Why?

https://cwe.mitre.org/data/definitions/426.html

Checklist

1. Closes

2. How was this tested:

3. Any docs updates needed?

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Note

Medium Risk
Primarily dependency/toolchain upgrades (notably OpenTelemetry) which can introduce subtle behavioral or compatibility changes; code changes are limited to test robustness.

Overview
Upgrades dependency sets across contrib/datadog, contrib/opentelemetry, and test modules, including OpenTelemetry (go.opentelemetry.io/otel/*) to v1.40.0, go.opentelemetry.io/auto/sdk to v1.2.1, and various supporting libs (e.g. testify, goleak, go-cmp, x/sys), updating go.sum accordingly.

Moves affected modules to Go 1.24 (and updates toolchain directives where present). Also hardens flaky tests: adds a nil guard around d.SearchAttributes in schedule integration assertions and retries starting a workflow with a pinned deployment version until the matching engine observes the poller.

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