feat(maui): catch up public API with Flutter observability SDK

[abelonogov-ld]

Stacked on #791. Review that first; this PR's diff is only the API work on top of it.

Summary

Brings the MAUI public API closer to the Flutter observability SDK. Every option below already existed in the native Android and iOS SDKs. MAUI simply didn't expose it, so this is mostly plumbing through the Kotlin and Swift bridges and the binding definitions.

Observability options

• CustomHeaders — extra headers sent with OTLP export.
• LogsApiLevel — minimum severity for logs sent through LDObserve.RecordLog. Uses a new ObservabilityLogLevel enum that follows the OpenTelemetry severity numbers (Trace = 1 … Fatal4 = 24), plus None to turn logging off. The default is Info.
• ServiceVersion now defaults to null and resolves to the app's version (AppInfo.Current.VersionString) instead of a hardcoded constant. DefaultServiceVersion is marked [Obsolete]. Behavior change: apps that don't set it now report their real version.
• LDObserve.NativeVersion — the version of the underlying native SDK, useful in support requests.

Session replay options

• Capture: SampleRate, FrameRate, Scale, ImageQuality (defaults 1.0 / 1.0 / 1.0 / 0.3, the same as native).
• Privacy: MinimumAlpha is now passed through on iOS too.
• LDIgnore() view extension, next to the existing LDMask() / LDUnmask().

On Android, "ignore" maps to mask, because the native Android SDK has no per-view ignore. The README says so.

Docs

The README now covers the new options, capture settings and NativeVersion.

Not in this PR

• Type-based privacy rules (MaskViewTypes, UnmaskViewTypes, IgnoreViewTypes) moved to the feat/maui-privacy-view-types branch, stacked on this one, so they can be reviewed separately.
• LDReplay.TrackEvaluation is effectively dead: nothing calls it, there's no native entry point, and evaluations are already recorded as evaluation spans by the observability hook. I suggest marking it [Obsolete] separately.
• Remaining Flutter-parity gaps: init readiness result, Shutdown(), Track / TrackScreenView / TrackClick, WithSpan, log capture, and the analytics / traces / metricsEnabled toggles.
• The Android bridge passes Analytics(screenViews = false) because MAUI is meant to report screen views itself, but MAUI never does. So Android currently records no screen views. Worth a follow-up.

Verification

• Built the sample on Android and iOS, and checked the new fields in the generated Android binding and in the rebuilt xcframework.
• After fix(maui): .NET 10 Android Release build fixes (relocate okio/okhttp) #791 dropped the OTel upgrade, rebuilt the Android binding cleanly against the reverted observability-android. CustomHeaders, LogsApiLevel and SampleRate are all present in the generated C#.
• Not verified on a device: CustomHeaders arriving on export.

---

Note

Overview
Expands the MAUI observability SDK so more native settings are configurable from .NET and documented, aligning with the Flutter SDK.

Observability: Adds CustomHeaders and LogsApiLevel (new ObservabilityLogLevel enum, OTel severities plus None). ServiceVersion is optional and, when unset, resolves to AppInfo.Current.VersionString instead of a fixed default (DefaultServiceVersion is obsolete). Exposes LDObserve.NativeVersion after init. Values are passed through the Android and iOS bridges.

Session replay: Adds capture knobs SampleRate, FrameRate, Scale, and ImageQuality, and wires Privacy.MinimumAlpha through on iOS. Adds View.LDIgnore() (Android falls back to mask). README covers observability options, capture settings, masking timing, and NativeVersion.

Package version bumps to 0.14.1.

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