[codex] Isolate kline interval exchange dialects

[createMonster]

Summary

• Remove exchange-specific kline interval formatter methods from the shared KlineInterval type.
• Move interval string conversion into exchange modules for Binance, Binance perpetual, Bybit perpetual, Backpack, and Paradex.
• Update REST and WebSocket call sites to use exchange-local conversion helpers.
• Refresh docs/ARCHITECTURE.md so it describes KlineInterval as a semantic core type rather than an API dialect surface.

Root Cause

KlineInterval mixed shared domain meaning with exchange API string dialects. Several exchange modules also modeled their dialects as extension traits on the shared type, which kept the same coupling pattern outside of core.

Validation

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --all-features
• cargo doc --no-deps --document-private-items --all-features
• cargo audit exits 0 with existing allowed warnings for dotenv, rustls-pemfile, keccak, and rand
• cargo run