chore: align Rust toolchains on 1.98.1

[Dzejkop]

Align Bedrock's repository toolchain, CI, cargo-deny, and release workflows on Rust 1.98.1 for the shared rollout instead of mixing Rust 1.94.1 with floating stable jobs.

Retain the original upgrade's behavior-preserving Clippy fix, use fixed-size result chunks for the paymaster migration, and replace test-only constant format! calls as required by Rust 1.98. Dependencies and runtime behavior are unchanged.

Validation

• cargo +1.98.1 fmt --all -- --check
• cargo +1.98.1 clippy --workspace --all-targets --all-features -- -D warnings
• Paymaster migration unit tests: 3 passed
• git diff --check

The matching Foundry integration test built but could not start because the local Foundry executable is unavailable. Full integration tests and Swift/Kotlin builds remain for CI.

Rollout dependency

Keep this PR in draft until Infrastructure #48339, WalletKit #509, Oxide #1190, Biometric Engines #648, and Flamingo #104 are ready. Version alignment will intentionally fail while the organization variable remains 1.94.1. No live variable or infrastructure change is made here.

AI usage/prompt(s)

Codex: “Adjust the coordinated Rust upgrade PRs to align on Rust 1.98.1, validate compatibility, and include Flamingo now that it participates in organization version alignment.”

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Note

Low Risk
Toolchain and CI pinning plus style-level Rust fixes; no dependency or production logic changes beyond equivalent duration/chunking APIs.

Overview
Pins Bedrock to Rust 1.98.1 end-to-end: rust-toolchain.toml moves from 1.94.1, and CI, cargo-deny, and release workflows stop using floating stable in favor of the same fixed version.

Small 1.98 / Clippy compatibility tweaks with no intended behavior change: Turnkey migration timeout is expressed via Duration::from_mins(3) instead of 180 seconds; paymaster migration pairs multicall results with as_chunks::<2>() instead of chunks_exact(2); smart-account tests compare against string literals with .to_string() rather than format! on constants.

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