Epic: De-duplicate interpreter runtime value-type wrappers

[nickna]

Goal

The interpreter-side twin of Epic 5: the runtime value-type wrappers (SharpTS*) were authored by copy-paste and need shared bases/helpers. The Intl family, crypto family, typed-array subclasses, and stream write-side each re-roll coercion, encoding, options-parsing, and member dispatch. Some copies have already diverged (e.g. Decipher.FormatOutput has a utf8 case Cipher lacks; forked ToDouble defaults) — an active latent-bug hazard, not cosmetic.

Start with the zero-risk static-helper extractions, then the abstract bases.

Sub-issues (rough priority order)

• Replace scattered ToDouble/ToInt copies with the canonical coercion #1134 — Canonicalize ToDouble/ToInt (6 copies reinvent Interpreter.ToNumber). Zero-risk start.
• Crypto: extract CryptoEncoding/CryptoAlgorithms + a SharpTSAesBase for Cipher/Decipher #1135 — Crypto helpers + SharpTSAesBase (Cipher/Decipher already diverged; encoder ×7).
• Add a SharpTSIntlFormatterBase (8 formatters repeat ~250-300 lines) #1136 — SharpTSIntlFormatterBase (8 formatters repeat locale/options/coercion).
• Hoist typed-array Slice/Subarray to the base (byte-identical x11) #1137 — Hoist typed-array Slice/Subarray to the base (~260 lines ×11).
• Extract a WritableCore shared by SharpTSWritable and SharpTSDuplex #1138 — WritableCore shared by Writable/Duplex (~200 lines re-implemented).
• Unify the member-dispatch contract (GetMember vs GetProperty vs Get) #1139 — Unify member dispatch (GetMember non-virtual, ~25 new shadows). Stage it.

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Working agreement for every child PR

• Green on dotnet test, SharpTS.Test262, and SharpTS.TypeScriptConformance (no baseline regression).
• Interpreter and compiled output must remain behaviourally identical; add dual-mode tests where applicable.
• Standalone compiled DLLs must not gain a SharpTS.dll dependency (see CLAUDE.md "Standalone DLL Constraint").

Source: codebase-wide maintainability audit, 2026-06-29.

[nickna]

All six sub-issues (#1134–#1139) implemented and merged in PR #1184 (main @ c60eb8d).

• Replace scattered ToDouble/ToInt copies with the canonical coercion #1134 canonicalize ToDouble/ToInt onto Interpreter.ToNumber
• Crypto: extract CryptoEncoding/CryptoAlgorithms + a SharpTSAesBase for Cipher/Decipher #1135 CryptoEncoding/CryptoAlgorithms + SharpTSAesBase
• Add a SharpTSIntlFormatterBase (8 formatters repeat ~250-300 lines) #1136 SharpTSIntlFormatterBase
• Hoist typed-array Slice/Subarray to the base (byte-identical x11) #1137 hoist typed-array Slice/Subarray to the base
• Extract a WritableCore shared by SharpTSWritable and SharpTSDuplex #1138 WritableCore + StreamArgs
• Unify the member-dispatch contract (GetMember vs GetProperty vs Get) #1139 IMemberProvider + virtual GetMember (36 new→override)

Validation: full xUnit 14813/0, TypeScriptConformance 31/0, Test262 0 baseline regressions (interp + compiled). Interpreter/compiled parity preserved; no new SharpTS.dll dependency in standalone output.