Modernize dependency injection and JSON serialization

[niemyjski]

Summary

• replace the vendored Newtonsoft.Json fork with System.Text.Json
• replace TinyIoC with Microsoft.Extensions.DependencyInjection while preserving the existing resolver API
• add source-generated serialization metadata, trimming annotations, and package/host NativeAOT smoke tests
• preserve legacy payload behavior for exclusions, depth, cycles, raw DataDictionary values, named floating-point values, public fields, and the Exceptionless ignore attribute
• honor STJ property contracts in filtered serialization, including ignore predicates, custom converters, number handling, extension data, and declared-type depth behavior
• isolate Generic Host and logging clients so provider-owned clients cannot mutate or dispose the process-wide default client
• collect and upload Cobertura coverage in Linux CI

Strict review hardening

• detect constructor and factory DI cycles deterministically without hanging
• scope cycle tracking to each logical resolution flow so concurrent use of a captured Microsoft service provider cannot produce false circular-dependency failures
• keep failed extended-data serialization diagnostics as strings instead of incorrectly marking them as raw JSON, including MessagePack round trips
• retain the public getter-only ClientConfiguration.Settings contract while allowing source-generated STJ deserialization
• apply the legacy ignore attribute at the filtered writer boundary without mutating caller-owned JsonTypeInfo
• prevent null or unstructured POST data from recursively invoking its converter
• split the oversized serializer test class into a partial compatibility-focused file
• declare the existing root Markdown documentation as the modern NuGet package readme while retaining the legacy readme.txt

Why

The original Newtonsoft.Json + TinyIoC client did not work under NativeAOT. Changing only the serializer or only the DI container was also insufficient: serializer metadata, DI activation, custom payload metadata, configuration activation, and runtime stack-frame handling all needed coordinated hardening.

Impact

• ApiCompat is clean for prior netstandard2.0 -> current netstandard2.0/net8.0 and prior net462 -> current net462.
• Custom payloads follow System.Text.Json contracts. Consumers relying on Newtonsoft-specific DataContract/DataMember behavior should migrate to STJ attributes and register source-generated metadata for NativeAOT payloads.
• Microsoft.Extensions.DependencyInjection becomes transitive. System.Text.Json 10 is used on net462, netstandard2.0, and net8.0.
• The DI container remains isolated per Exceptionless client; an application's root provider is not imported automatically.
• Configuration-based hosting and logging overloads now own isolated clients. Explicit client overloads remain caller-owned. Code that intentionally relied on those overloads mutating ExceptionlessClient.Default will observe the corrected isolated behavior.
• The package adds modern target assets and NativeAOT support. It is about 17% larger overall because it contains more TFMs and the package readme, while the individual netstandard2.0 assembly is about 65% smaller after removing the vendored Newtonsoft source.
• Modern target assets use normal runtime stack traces instead of the legacy IL/PDB demystifier.
• This should ship as 7.0 because serializer semantics, dependencies, target assets, ownership behavior, and modern stack-trace behavior change even though the public API check is clean.

Validation

• definitive non-Windows suite: 377 core tests + 13 MessagePack tests passed; 0 failed; 18 existing skips
• Cobertura: 74.2% line / 50.1% branch overall; 88.9% of changed executable production lines covered
• critical coverage: filtered writer 97.2% line / 92.5% branch, DataDictionary 98.9% / 92.0%, JSON element conversion 95.7% / 95.7%, DI resolver 85.8% / 64.5%, and DI fallback 89.5% / 80.0%
• Windows-shaped full solution build: net462, net472, netstandard2.0, net8.0, net8.0-windows, net9.0, and net10.0; 0 warnings, 0 errors
• uniquely versioned packed-package NativeAOT executables: net8.0 and net10.0 passed, including default DI, built-in configuration deserialization, source-generated custom payload converters/fields, compatibility-ignore filtering, storage, queues, submission, batches, and exception frames
• Generic Host NativeAOT executables: net8.0 and net10.0 passed
• current direct and transitive NuGet vulnerability audit: no vulnerable packages
• final NuGet pack: passed without warnings; both README.md and legacy readme.txt are present
• git diff --check: passed; no changed C# file exceeds 1,000 lines

Historical NativeAOT result

State	Result
Newtonsoft.Json + TinyIoC	published with 10 warnings, then failed at runtime
System.Text.Json + TinyIoC	still failed
System.Text.Json + Microsoft DI before AOT hardening	4 DI warnings, then the serializer constructor was trimmed
Hardened System.Text.Json + Microsoft DI	package and host executables pass on net8.0 and net10.0 with ILLink/trim-analysis warnings treated as errors

CI status

• Linux, macOS, and Windows passed in both push and pull-request workflows on commit d94a17b
• CLA passed; no review comments or unresolved threads

Follow-up

• consider requiring the platform build checks in branch protection; currently only license/cla is required
• the PR remains draft for maintainer review of the 7.0 release and ownership changes