[Repo Assist] Refactor: extract mkGenericType helper, eliminate 10-fold SynType.App duplication

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Summary

Closes #274

Adds a private mkGenericType helper in AstExtensions.fs that consolidates the repeated SynType.App construction pattern across 10 extension members (Option, ResizeArray, Set, NativePointer, Option(string), Dictionary, Map, List(SynType), Array, List(string)).

Root Cause

Ten SynType with extension members each inlined an identical 8–10 line SynType.App(...) call with the same boilerplate arguments, resulting in ~100 lines of near-identical structural duplication. A SynType.CreateApp helper already existed (line 195) but used dotsOrCommas args for commaRanges and Some range0 for both angle ranges — incompatible with the postfix Array member which intentionally uses greaterRange=None; lessRange=None.

Fix

Added to AstExtensions.fs (module-level, alongside the existing dotsOrCommas private helper):

/// Builds a generic SynType.App node. Use hasAngles=false only for postfix array syntax.
let private mkGenericType (typeName: SynType) (typeArgs: SynType list) (isPostfix: bool) (hasAngles: bool) =
    SynType.App(
        typeName = typeName,
        typeArgs = typeArgs,
        commaRanges = [],
        isPostfix = isPostfix,
        range = range0,
        greaterRange = (if hasAngles then Some range0 else None),
        lessRange  = (if hasAngles then Some range0 else None)
    )

All 10 call sites replaced with one-liners using mkGenericType.

Trade-offs

• Benefit: single source of truth for commaRanges = [] default and angle-bracket convention; Array's intentional no-angle-bracket exception is now explicit via hasAngles=false rather than hiding in copy-pasted code; ~90 lines of boilerplate removed.
• Risk: none — semantics are identical at all 10 call sites; commaRanges = [] was already consistent across all of them.

Test Status

✅ Build succeeded (0 warnings, 0 errors)
✅ 33/33 integration tests passed

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Pull request overview

Refactors AstExtensions to reduce duplicated SynType.App boilerplate by introducing a shared helper for constructing generic SynType application nodes, while preserving the existing special-case behavior for postfix array syntax.

Changes:

• Added a private mkGenericType helper that centralizes SynType.App construction defaults (notably commaRanges=[] and configurable angle bracket ranges).
• Updated the 10 SynType extension members (e.g., Option, List, Map, Dictionary, Array) to delegate to mkGenericType, eliminating repeated inline SynType.App(...) blocks.

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