handle group capsule tag collisions

[mcjkula]

Summary

• 0x15 group decrypt treated a one-byte capsule view-tag match as authoritative, so a tag collision could stop on the wrong capsule and return decryption failure.
• Rust, Python, TypeScript, and Go now try every matching capsule and return plaintext only after AEAD authentication succeeds.
• Removed private first-match capsule scanners in Rust, TypeScript, and Go so production decrypt has one capsule-selection path.
• Added deterministic collision regressions in all four SDKs for both known member count and trial parsing.

Test plan

• cargo test — 252 Rust tests passed
• cargo clippy --tests -- -D warnings — Rust warnings denied
• pytest tests/ — 207 Python tests passed after rebuilding samp-crypto in the root .venv
• npm test — 206 TypeScript tests passed
• go test ./... — Go test suite passed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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