perf(dart): typed-container write fast path with scan elimination

[yash-agarwa-l]

Why?

Writing List<T> / Set<T> struct fields paid an O(n) scan to detect heterogeneous types and nulls. Codegen already knows the element type is concrete and non-nullable — the scan is pure overhead.

What does this PR do?

• Adds writeTypedListPayload<T> / writeTypedSetPayload<T> that resolve TypeInfo once and write the header/type-meta without scanning.
• Adds writeGeneratedDirectListValue<T> / writeGeneratedDirectSetValue<T> generated-code entry points.
• Adds a codegen predicate (gated on real Dart DartType nullability) that emits the fast path for non-nullable, non-ref, non-dynamic list/set fields; everything else keeps the existing slow path.

Related issues

#3558

AI Contribution Checklist

• Substantial AI assistance was used in this PR: yes / no
• If yes, I included a completed AI Contribution Checklist in this PR description and the required AI Usage Disclosure.
• If yes, my PR description includes the required ai_review summary and screenshot evidence of the final clean AI review results from both fresh reviewers on the current PR diff or current HEAD after the latest code changes.

Does this PR introduce any user-facing change?

• Does this PR introduce any public API change?
• Does this PR introduce any binary protocol compatibility change?
  No user-facing or wire-format change. Serialized bytes are byte-identical to main.

Benchmark

Datatype	Operation	Fory TPS	Protobuf TPS	Fastest
Struct	Serialize	4,696,615	1,998,625	fory (2.35x)
Struct	Deserialize	5,815,245	4,173,568	fory (1.39x)
Sample	Serialize	1,744,871	481,801	fory (3.62x)
Sample	Deserialize	2,007,877	780,317	fory (2.57x)
MediaContent	Serialize	944,111	398,324	fory (2.37x)
MediaContent	Deserialize	1,457,065	675,724	fory (2.16x)
StructList	Serialize	1,981,716	351,853	fory (5.63x)
StructList	Deserialize	2,261,436	596,027	fory (3.79x)
SampleList	Serialize	426,153	46,590	fory (9.15x)
SampleList	Deserialize	479,900	99,694	fory (4.81x)
MediaContentList	Serialize	220,342	76,330	fory (2.89x)
MediaContentList	Deserialize	341,839	131,730	fory (2.60x)

[chaokunyang]

@yash-agarwa-l Could you merge main branch, I've refactored fory dart to support dart web

[yash-agarwa-l]

@yash-agarwa-l Could you merge main branch, I've refactored fory dart to support dart web

I will do

[chaokunyang]

LGTM