Port v0.57.0: harden OpenCodex numeric and cache parsing

[Finesssee]

What changed

Ports upstream v0.57.0 commit b1e27d266a8e1a0db991be7cf40526f12e6a4e1d (fix: reject unrepresentable numeric usage safely (#3486)) into the Windows OpenCodex spend path.

• Rejects the rounded floating-point 2^64 boundary before the u64 cast while preserving exact JSON integer u64::MAX.
• Adds parser version 1 to the OpenCodex parse cursor and forces a full reparse for missing or mismatched versions.
• Keeps CACHE_SCHEMA_VERSION = 2; this is parser compatibility gating, not a cache container format change.

Scope

• rust/src/spend_contract/opencodex.rs
• rust/src/spend_contract/opencodex/cache.rs

This is a stacked micro-PR after #488, with base branch port/micro-0.57.0-codex-whitespace. It does not change the app version, release files, CI, or later upstream versions.

Validation

• cargo fmt --all -- --check — passed
• git diff --check — passed
• Focused Rust test and cargo check --manifest-path rust/Cargo.toml --tests — attempted, but blocked before test execution because this host has no MSVC cl.exe; where.exe resolves Git's usr/bin/link.exe, so rustc fails in linking.
• Oracle review — approved the numeric boundary, parser-version migration, test coverage, PR scope, and published stack.

Upstream reference

• Commit: b1e27d266a8e1a0db991be7cf40526f12e6a4e1d
• Release range: v0.56.8...v0.57.0

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