New optional params: twapOrder.details, reserveRequestWeight.destination, marginTable.dex

[joeblau]

Problem

Three new optional parameters (upstream nktkas#170, nktkas#178, nktkas#186):

• twapOrder optional details param carrying trigger (t) and stop (s) prices — enables trigger TWAPs.
• reserveRequestWeight optional destination — pay weight on behalf of another user; skipped in action hashing when unset (documented on the exchange-endpoint page).
• marginTable optional dex param.

Note the signing impact: twapOrder.details and reserveRequestWeight.destination affect the action hash, so the L1 msgpack encoding must include them when set (and exclude destination when unset, per the docs).

Fix

Add the params to the request schemas and the msgpack/canonicalization path; test both set and unset signing output.