[ALNR-6808] Remove ProjectRateV2 methods from lbox-alignerr SDK

[pawelkozik-labelbox]

https://labelbox.atlassian.net/browse/ALNR-6808

Context

• lbox-alignerr still wraps legacy Pay By Role GraphQL (setProjectRateV2 / ratesV2)
• All live boost projects are on Pay By Activity; UI role-rate config is gone
• SDK clients must stop calling those ops before LB-API write removal (ALNR-6809)

In scope

• Remove ProjectRateV2 schema and builder/factory rate wiring from lbox-alignerr
• Old rate entry points raise a clear error directing callers to the Rates UI (Pay By Activity)
• Project create still works without setting rates (project-owner validation remains)
• Bump package to 0.3.0

Out of scope

• Activity-rate SDK wrappers
• LB-API GraphQL / Alignerr billing materialization deletion

---

Note

Medium Risk
Breaking SDK change for anyone still setting or reading Pay By Role rates via Python/YAML; project creation behavior changes (no automatic rate setup). Billing-critical but intentional and surfaced with clear errors.

Overview
Removes legacy Pay By Role rate APIs from lbox-alignerr ahead of LB-API write removal. The ProjectRateV2 schema module is deleted; builder/factory no longer wire rates on create, and alignerr/customer rate validation is dropped (project owner validation remains).

Callers hitting old entry points get explicit failures: get_project_rates / set_project_rate and builder set_alignerr_role_rate / set_customer_rate raise NotImplementedError with a shared message pointing to the Labelbox Rates UI (Pay By Activity). YAML configs that include rates or customer_rate fail fast with ValueError using the same message.

Package version bumps to 0.3.0; README no longer lists rate management; tests and fixtures are updated to match.

^{Reviewed by Cursor Bugbot for commit 9fd23ab. Bugbot is set up for automated code reviews on this repo. Configure here.}