Add native argument encoding

[scarmuega]

Summary

• add one recursive ParamType-directed native Swift argument encoder
• preserve signed-i128 integer precision, canonical Data encoding, record/variant order, deterministic maps, and JSON passthrough
• expose case-insensitive parameter lookup and the generated-client argTagged seam
• copy and execute every pinned complex wire accept/reject vector

Verification

• swift package resolve
• swift format lint --strict --recursive Sources Tests Package.swift
• swift build --configuration debug
• swift test --filter Tx3SDKTests --parallel (19 tests)
• swift build --package-path examples/consumer
• xcodebuild -scheme tx3-swift-sdk -destination platform=iOS Simulator,name=iPhone 17 Pro,OS=26.2 test (19 unit tests; live E2E skipped by design)
• git diff --check
• wire-vectors.json SHA-256: 9d16d23a06a36a7ec1eb07af14f0b404b54f1438bb88692dc13ed9c078422a2b

[scarmuega]

Rework verification at 7840a89:

• Preserves native passthrough integer meaning by rejecting Int and Int64 values that cannot be represented exactly by JSONValue.number.
• Carries full nested argument paths and expected kinds for signed-i128 range failures and passthrough conversion failures.
• Adds regressions for a nested out-of-range BigInt and a nested Int64 above binary64 exact-integer range.

Passed locally: swift package resolve; strict recursive swift-format lint; debug build; Tx3SDKTests in parallel (20 tests); external consumer build; iPhone 17 Pro / iOS 26.2 simulator suite (20 unit tests, live credentialed E2E skipped); git diff --check. The pinned wire-vector fixture remains SHA-256 9d16d23a06a36a7ec1eb07af14f0b404b54f1438bb88692dc13ed9c078422a2b.

GitHub CI run 36150915498 passed at this exact head, including Xcode 16.4 build, formatting, unit tests, iOS 18 simulator tests, and external consumer build.

[scarmuega]

Ready for your review.

Plan: plans/swift-sdk-argument-encoding.md
QA-approved head: 7840a8967ac2e5b33774aaa7bf0e7a3704c3f9e1

Review this PR now. Merge it to accept; Trellis will observe the merge, integrate the domain pin, and retire the plan. Request changes to send work back through QA. Agents do not merge.