ci/cargo-test

[kimcascante]

Summary

Adds support for a Minimum Supported Rust Version (MSRV) and validates it in CI.

Closes #163

Changes

• Defined MSRV: Rust 1.74.0 in Cargo.toml
• Extended existing CI workflow to test both MSRV and stable
• Added wasm32-unknown-unknown target validation
• Documented local development instructions in README

Scope

• CI-only changes
• No modifications to contract logic
• No impact on on-chain behavior

Security Notes

• Ensures reproducible builds for auditors
• No changes to contract execution paths
• No new dependencies introduced

Testing

• CI runs on:
  • Rust 1.74.0 (MSRV)
  • Rust stable
• Existing test suite passes in both environments

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@kimcascante Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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