feat(bindings): generate native platform adapters

[glennawatson]

Summary

Generate native platform bindings through separate affinity-based plugins.

• Select observation, conversion, command and collection-write mechanisms from the consumer's framework types using interface-based plugins and shared static helpers.
• Support WPF, WinForms, MAUI, WinUI/Uno, Android, Apple and Blazor mechanisms inside the source generator, with helpers emitted only for bindings that use them.
• Preserve higher-affinity custom providers with property-specific cached selection and refresh support; generated mechanisms win ties, and legacy expressions and object adapters are created only for winning custom providers.
• Keep generated getters, delivery, comparisons, conversions and setters typed, including nullable, visibility, date and string conversions.
• Bind native commands with command/control replacement, parameters, enabled state and disposal, and populate WinForms control collections through native setters.
• Reduce generator allocations and avoid per-update collection-array copies and boxing on common generated paths; public object-valued contracts retain their required boundaries.
• Validate native adapter behavior and allocations through existing test and benchmark projects, targeting .NET 10/11 with NativeAOT runs and GcVerbose traces.
• Document native-event bindings and benefits for ordinary JIT applications.

Why

Generated bindings need ReactiveUI's platform behavior and custom-provider precedence.

• Compile-time knowledge of supported mechanisms allows direct typed bindings while preserving runtime registrations that outrank the generated choice.

Breaking changes

None.

How this was verified

Solution builds and tests exercise generated bindings, native contracts, custom-provider precedence and refresh.

• Generation and runtime benchmarks exercise .NET 10/11 and NativeAOT; GcVerbose traces check allocation behavior. Native benchmark fixtures measure managed wiring rather than platform rendering.

Notes for the reviewer

Start with plugin selection and the custom-provider boundary.

• Review Plugins, per-invocation emission, ObservationAffinityChecker, and typed conversion and collection-write helpers; generated snapshots and public API baselines are mechanical.
• Pay particular attention to per-property affinity, generated tie precedence, refresh races, and expressions being constructed only after a custom provider wins.

Checklist

• I have read the Contribute guide
• The PR title follows Conventional Commits
• Tests cover this change, or the summary says why they do not
• New or changed public API has XML documentation

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
94.1% Coverage on New Code
3.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 93.79892% with 103 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.59%. Comparing base (e57d96e) to head (56e43c8).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...rs/Plugins/Observation/AndroidObservationPlugin.cs	59.37%	10 Missing and 3 partials ⚠️
...ors/Plugins/SetMethod/WinFormsCollectionSymbols.cs	68.18%	3 Missing and 4 partials ⚠️
...ceGenerators/CodeGeneration/BindToCodeGenerator.cs	79.31%	6 Missing ⚠️
...urceGenerators/CodeGeneration/ConversionEmitter.cs	90.76%	5 Missing and 1 partial ⚠️
...rators/Plugins/Conversion/AppleConversionPlugin.cs	77.77%	2 Missing and 4 partials ⚠️
...rators/Plugins/Observation/UnoObservationPlugin.cs	40.00%	5 Missing and 1 partial ⚠️
...eGenerators/Plugins/Observation/PlatformSymbols.cs	84.84%	5 Missing ⚠️
...rceGenerators/Plugins/ObservationPluginRegistry.cs	79.16%	5 Missing ⚠️
...ors/Plugins/Observation/AppKitObservationPlugin.cs	73.33%	2 Missing and 2 partials ⚠️
...rators/Plugins/Observation/KVOObservationPlugin.cs	83.33%	1 Missing and 3 partials ⚠️
... and 23 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #111      +/-   ##
==========================================
- Coverage   99.75%   97.59%   -2.16%     
==========================================
  Files         292      349      +57     
  Lines       11786    12539     +753     
  Branches     1277     1495     +218     
==========================================
+ Hits        11757    12238     +481     
- Misses         17      245     +228     
- Partials       12       56      +44     

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