feat(exchange): add bulk_order_with_grouping for normalTpsl atomic submits

[HathorNodes]

Summary

The current `bulk_order` and `bulk_order_with_builder` hardcode `grouping: "na"` with no caller-facing override, which makes it impossible to submit atomic IOC entry + paired SL trigger via `grouping="normalTpsl"` — the canonical HL TPSL pattern that the Python SDK exposes as `exchange.bulk_orders(orders, grouping=...)`.

This PR adds two new methods to expose the existing `BulkOrder { grouping }` field through the public API:

• `bulk_order_with_grouping(orders, wallet, grouping: &str)` — same payload shape as `bulk_order`, with `grouping` threaded through.
• `bulk_order_with_builder_and_grouping(orders, wallet, builder, grouping: &str)` — equivalent with builder fees.

Existing `bulk_order` / `bulk_order_with_builder` are preserved as thin shims delegating to the new methods with `grouping = "na"`, so this change is fully backward-compatible — zero call-site updates needed for current users.

Valid grouping values, per the L1 action schema: `"na"`, `"normalTpsl"`, `"positionTpsl"`.

Use case

Submitting a bracket order (entry IOC + paired stop-loss trigger) as a single signed L1 action so they're processed atomically by the matching engine — eliminates the race where an entry could fill into an unprotected position momentarily if the SL trigger were posted separately. The Python SDK has supported this since 2023; this brings the Rust SDK to parity.

Test plan

• `cargo build` green
• `cargo test --lib` green (8 tests pass; the patch only adds methods, no behaviour changes for existing tests)
• Integrated into the Hathor Hyperliquid trading bot's Rust port via `[patch.crates-io]` — 101 workspace tests + cross-language parity tests against the Python SDK all green using the new method to post `normalTpsl` brackets.

Happy to add unit tests for the grouping field if the maintainers prefer — the existing test suite doesn't cover `bulk_order` shape directly so wanted to confirm convention before adding.