refactor(client): allow turbofish with multiple Instructions

[nxsaken]

Description

Converts impl Instruction to an explicit type parameter in functions accepting multiple instructions.

Benefits

Lets users avoid converting heterogeneous instructions to InstructionBoxes in a separate variable before submitting to a client, which is more ergonomic.

Checklist

• I've read CONTRIBUTING.md
• I've used the standard signed-off commit format (or will squash just before merging)
• All applicable CI checks pass (or I promised to make them pass later)
• (optional) I've written unit tests for the code changes
• I replied to all comments after code review, marking all implemented changes with thumbs up