chore: declare rust-version and forbid unsafe_code in manifests

[e-desouza]

Why

Two hardening gaps were identified in the manifest files:

1. No declared MSRV — Cargo.toml had no rust-version field, so the documented MSRV of 1.87 was unenforced. xrpl-rust-macros uses edition = "2024" (requires Rust ≥ 1.85) with no corresponding guard. Downstream users on older toolchains received cryptic proc-macro errors instead of a clear MSRV message. Closes chore: declare rust-version = "1.87" in Cargo.toml (MSRV enforcement) #351.

2. No unsafe_code lint guard — The crate contains no unsafe blocks, but without forbid(unsafe_code) nothing prevents a future contribution from silently adding raw pointer operations into deserialization paths that process untrusted XRPL network data. Closes chore: add [lints] table with unsafe_code = "forbid" to Cargo.toml #350.

What changed

• Cargo.toml: added rust-version = "1.87" and [lints.rust] unsafe_code = "forbid"
• xrpl-rust-macros/Cargo.toml: added rust-version = "1.85" (matches edition = "2024" requirement)

How to validate

# MSRV guard works
rustup toolchain install 1.86
cargo +1.86 check 2>&1 | grep "rust-version"
# → error: package `xrpl-rust v1.2.0` cannot be built because it requires rustc >= 1.87.0

# unsafe_code guard works
# Add `unsafe { }` anywhere in src/ and verify:
# → error: usage of an `unsafe` block

# Normal build still works
cargo check --all-features
cargo clippy --all-features -- -D warnings

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.71%. Comparing base (c83df4f) to head (01f4002).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #352   +/-   ##
=======================================
  Coverage   86.71%   86.71%           
=======================================
  Files         252      252           
  Lines       32630    32630           
=======================================
  Hits        28296    28296           
  Misses       4334     4334           

Flag	Coverage Δ
integration	71.32% <ø> (ø)
unit	87.33% <ø> (ø)

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[Copilot]

Pull request overview

This PR hardens the crate manifests by enforcing explicit MSRV constraints via rust-version and preventing introduction of unsafe blocks via Cargo’s manifest lint configuration.

Changes:

• Added rust-version = "1.87" to the root xrpl-rust manifest to enforce the documented MSRV.
• Added rust-version = "1.85" to xrpl-rust-macros to match the Rust 2024 edition minimum requirement.
• Added [lints.rust] unsafe_code = "forbid" to the root manifest to prevent unsafe code from compiling.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
Cargo.toml	Enforces MSRV 1.87 and forbids unsafe blocks via manifest lints.
xrpl-rust-macros/Cargo.toml	Adds an explicit MSRV guard for the proc-macro crate (Rust 1.85 for edition 2024).

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[e-desouza]

Fixed in 284aa4c: Added [lints.rust] unsafe_code = "forbid" to xrpl-rust-macros/Cargo.toml. Both crates now declare the lint gate.