fix: update outdated MSRV comment in is_exact_integer

[hobostay]

Summary

• Updates the outdated MSRV comment in buffa/src/json_helpers.rs from "1.81" to "1.85" to match the actual rust-version specified in Cargo.toml.

The comment in is_exact_integer() stated the MSRV was 1.81, but the workspace Cargo.toml has specified rust-version = "1.85" since the beginning of the 0.3.x series.

Test plan

• Verified Cargo.toml rust-version is "1.85"
• Grep confirms this was the only reference to "MSRV 1.81" in the codebase

🤖 Generated with Claude Code

[github-actions]

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[hobostay]

I have read the CLA Document and I hereby sign the CLA

[iainmcgin]

recheck

[iainmcgin]

[claude code] Amended the commit on your behalf with maintainer-can-modify push access — the original was authored as Test User <test@example.com>, which the CLA bot can't match to a GitHub account. The new commit is authored with your users.noreply.github.com email (GitHub's canonical privacy form), which resolves to your account.

recheck

[iainmcgin]

[claude code] One-line doc fix — updates stale MSRV reference from 1.81 to the actual workspace MSRV 1.85. The f64::trunc() / Rust 1.86 justification remains correct (MSRV 1.85 still can't use core's trunc). Thanks!