test: add crosstest package

[giortzisg]

Description

This PR adds the crosstest package for adding integration tests without polluting the root package go.mod. This also adds OTel link tests with http and logging frameworks.

Issues

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Reminders

• Add GH Issue ID & Linear ID
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

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Semver Impact of This PR

🟢 Patch (bug fixes)

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Breaking Changes 🛠

• Update compatibility policy to align with Go, supporting only the last two major Go versions. by giortzisg in #1264
• Drop support for Go 1.24 by giortzisg in #1264

Internal Changes 🔧

Deps

• Bump golangci-lint action from 2.1.1 to 2.11.4 by giortzisg in #1265
• Bump go.opentelemetry.io/otel/sdk from 1.40.0 to 1.43.0 in /otel by dependabot in #1256
• Bump go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp from 1.40.0 to 1.43.0 in /otel/otlp by dependabot in #1255

Other

• Add crosstest package by giortzisg in #1269

• Add sentrytest package by giortzisg in #1267

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