Fix json parsing of nullable/empty fields

[romtsn]

📜 Description

• Renames nextList to nestListOrNull to actually match what the method does
• Checks if there's any object in a collection before trying to parse it (which prevents the "Failed to deserilize object in list" log message)
• If a date can't be parsed as ISO timestamp, attempts to parse it as millis silently, without printing a log message
• If op is not defined as part of SpanContext, fallback to an empty string. This field is actually optional in the spec, but we made it non-optional, as we also use the same structure across the project everywhere, where the op field is actually required. So we just duct-tape it for hybrid SDKs here. See https://develop.sentry.dev/sdk/event-payloads/contexts/#trace-context

💡 Motivation and Context

Closes #2151
Closes getsentry/sentry-capacitor#450

💚 How did you test it?

Manually + automated

📝 Checklist

• I reviewed the submitted code.
• 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.
• 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

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	371.26 ms	443.66 ms	72.40 ms
Size	1.72 MiB	2.29 MiB	576.40 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
4d55d51	389.44 ms	471.55 ms	82.11 ms

App size

Revision	Plain	With Sentry	Diff
4d55d51	1.72 MiB	2.29 MiB	576.34 KiB

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
sentry/src/main/java/io/sentry/JsonSerializer.java	90.67% <100.00%> (ø)
...ry/src/main/java/io/sentry/ProfilingTraceData.java	78.51% <100.00%> (ø)
...entry/src/main/java/io/sentry/SentryBaseEvent.java	90.90% <100.00%> (ø)
sentry/src/main/java/io/sentry/SentryEvent.java	89.43% <100.00%> (ø)
sentry/src/main/java/io/sentry/SpanContext.java	83.43% <100.00%> (+2.71%)	⬆️
...main/java/io/sentry/clientreport/ClientReport.java	62.00% <100.00%> (ø)
...sentry/profilemeasurements/ProfileMeasurement.java	52.72% <100.00%> (ø)
...ry/src/main/java/io/sentry/protocol/DebugMeta.java	90.24% <100.00%> (ø)
...y/src/main/java/io/sentry/protocol/SdkVersion.java	65.34% <100.00%> (ø)
...main/java/io/sentry/protocol/SentryStackTrace.java	94.54% <100.00%> (+0.10%)	⬆️
... and 4 more

📢 Thoughts on this report? Let us know!.

[markushi]

Nice one, looks good to me!