Marshallable Core Interfaces & Base Classes

[peter-lawrey]

📝 What this PR does

A focused tidy-up of the core marshalling APIs

Area	Change	Why it matters
Null-safety	Marshallable.streamFromFile(Class<T>, String) is now annotated @NotNull instead of @Nullable. The method never returned null – the annotation now reflects reality.
API docs	Re-wrote and expanded Javadoc for: • Marshallable and its helpers • ReadMarshallable, WriteMarshallable, MarshallableIn • Trivially-copyable & config base classes • Annotation/utility types (AsMarshallable, KeyedMarshallable, …) • Deprecated DynamicEnum now states removal schedule	• Consistent first-line “intent” sentences (better IDE tooltips) • Clearer parameter/return contracts & exception notes • Practical examples and behavioural edge-cases • Explicit deprecation notice for DynamicEnum
Internal links & wording	Fixed typos, modernised language, removed outdated references (delta wire, legacy flags).	Easier onboarding; smaller learning curve.

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Commit map

Commit	Message	Highlight
1/7	Create the branch	@Nullable ➜ @NotNull for streamFromFile(Class, String)
2/7	Improve Marshallable Javadoc (#1031)	100-line rewrite, clearer utility docs
3/7	Improve marshallable interfaces Javadoc (#1032)	Full docs for Read/WriteMarshallable
4/7	Improve Javadoc for marshallable base classes (#1033)	Docs for BytesInBinaryMarshallable, SelfDescribingMarshallable, etc.
5/7	Improve Javadoc for configuration & trivially copyable classes (#1034)	Merge-aware config notes, schema-evolution notes
6/7	Document deprecation in DynamicEnum (#1035)	Clearly marked for removal in x.28
7/7	Improve MarshallableIn Javadoc (#1037)	Extensive read-side docs & intern limit note