[RUM-16384] feat: add nativeIosResourceTracking RUM option

[marco-saia-datadog]

What does this PR do?

Introduces an explicit RUM initialization option to enable/disable iOS resource tracking:

rumConfiguration: {
    nativeIosResourceTracking?: boolean
}

Motivation

On iOS, native URLSession resource tracking has been on by default since v3.2.0. It's enabled whenever firstPartyHosts is defined, and the JS default is an empty array [].

trackResources: false doesn't turn it off, so today the only workaround is to set firstPartyHosts to undefined, which also disables first-party tracing.

Changes

• JS: the option is added to RumConfiguration, DatadogProviderConfiguration, the async/partial init configs, FileBasedConfiguration and datadog-configuration.schema.json. No layer sets a default, so undefined reaches native unchanged.
• iOS: both parsers (JS bridge and native-init JSON) read the option. buildRumConfiguration now uses nativeIosResourceTracking ?? (firstPartyHosts != nil).
• Tests: Jest covers how the option flows through every config path. The new XCTests cover the 9 combinations of option value × firstPartyHosts (nil, [], non-empty), plus the parsers.

Compatibility

Existing apps see no behavior change unless they explicitly set the new option.

Testing

• Jest: 838 passed, 1 skipped
• iOS XCTests (DatadogSDKReactNative test scheme)

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• If this PR is auto-generated, please make sure also to manually update the code related to the change

[datadog-prod-us1-5]

✅ All CI checks and tests passed.

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

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