perf(core): [SDK Overhead Reduction 11] Replace ISO8601 timestamp handling

[adinauer]

PR Stack (SDK Overhead Reduction)

• perf(core): SDK Overhead Reduction #5499
• perf(core): [SDK Overhead Reduction 1] Skip java.specification.version lookup on Android #5500
• perf(android): [SDK Overhead Reduction 2] Replace reflective OptionsContainer with direct subclass #5501
• perf(android): [SDK Overhead Reduction 3] Reuse SentryExecutorService for DeviceInfoUtil pre-caching #5502
• perf(android): [SDK Overhead Reduction 4] Use default timezone directly #5587
• perf(core): [SDK Overhead Reduction 5] Replace Calendar with Date in DateUtils #5589
• perf(core): [SDK Overhead Reduction 6] Reduce JsonWriter stack allocation #5591
• perf(core): [SDK Overhead Reduction 7] Lazily allocate Breadcrumb data #5598
• perf(core): [SDK Overhead Reduction 8] Reduce context serialization allocations #5599
• perf(core): [SDK Overhead Reduction 9] Lazily allocate reflection serializer state #5600
• perf(core): [SDK Overhead Reduction 10] Lazily create reflection JSON serializer #5601
• perf(core): [SDK Overhead Reduction 11] Replace ISO8601 timestamp handling #5602
• perf(core): [SDK Overhead Reduction 12] Avoid cloning Date getters #5603

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📜 Description

Replaces the vendored ISO8601Utils timestamp parsing and formatting path used by DateUtils with a Sentry-specific ISO-8601 utility.

The new utility parses supported Sentry timestamp formats directly to epoch milliseconds and formats epoch milliseconds directly to UTC ISO-8601 strings. Breadcrumb serialization also formats millisecond-backed timestamps directly instead of materializing a Date first.

💡 Motivation and Context

Timestamp parsing and formatting are used on hot serialization/deserialization paths. The existing vendored implementation creates Calendar instances and intermediate date objects. This change reduces allocation overhead while preserving the existing DateUtils facade and supported timestamp formats.

💚 How did you test it?

• ./gradlew spotlessApply apiDump
• ./gradlew :sentry:test --tests io.sentry.DateUtilsTest --tests io.sentry.protocol.BreadcrumbSerializationTest --tests io.sentry.JsonObjectReaderTest --tests io.sentry.JsonObjectSerializerTest

📝 Checklist

• I added GH Issue ID & Linear ID
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

#skip-changelog

⚠️ Merge this PR using a merge commit (not squash). Only the collection branch is squash-merged into main.

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.43.1 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	313.85 ms	374.62 ms	60.77 ms
Size	0 B	0 B	0 B