Add linear constraint config to multi-poses-execution-switch

[NickPPC]

Summary

Adds an optional linear_constraint configuration to the multi-poses-execution-switch component, allowing the arm to be constrained to straight-line movements between poses. This gives more predictable end-effector paths for workflows like coffee brewing where wild joint-space trajectories are undesirable.

Changes

• multiposesexecutionswitch: Add LinearConstraintConf struct and optional linear_constraint field on Config. When set, a motionplan.LinearConstraint is passed to the motion planner via MoveReq.Constraints.
• go.mod: Promote go.viam.com/utils to a direct dependency (result of go mod tidy).
• README.md: Document the new linear_constraint config field, add a sub-table for its fields, and update the example configuration.

Testing

• Verified the module compiles cleanly with go build ./...
• Manual testing: configure linear_constraint with tolerance values and verify the arm moves in a straight line between poses

Claude Code Prompts Used

• "can you add a config in the multi-pose-execution-switch to set linear constraints for movement?"
• "can you update the appropriate readme section"
• "commit this, push it, and open a PR"