Add the blocks.validate Web API method to the Slack API client. Callers
can validate Block Kit payloads via methods().blocksValidate(req) (and the
async equivalent), passing blocks, message, or view as JSON-encoded
strings. No scopes are required.

Adds the endpoint constant, sync and async interface methods and impls,
the request form builder, the request/response model classes (with an
errors[] list of code/message/pointer/relatedComponent), the Tier3 rate
limit, a local test, and a response sample for type generation.

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

blocks.validate has special rate-limiting conditions rather than a standard
tier (see https://docs.slack.dev/reference/methods/blocks.validate), so model
it as SpecialTier_blocks_validate instead of Tier3. Regenerate the rate-limit
metadata so the committed rate_limit_tiers.json matches the generated output,
which also sorts blocks.validate into its correct alphabetical position — this
is what was tripping the CI tree-drift check.

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

Add a blocks_Test integration test under test_with_remote_apis that exercises
blocks.validate against the real API: a well-formed payload validates with no
errors, and a malformed payload surfaces the live validation feedback
(recording the actual contract — ok=false with an error, or ok=true with a
populated errors[] carrying code/message/pointer). Refresh the method-coverage
scrape marker in MethodsTest to reflect the current 310-endpoint list.

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

The method was consistently placed after the bookmarks family, but "blocks"
sorts before "bookmarks". Move every insertion site into alphabetical order:
request/response imports, the sync/async interface declarations and their
implementations, the RequestFormBuilder toForm mapping, the rate-limit tier
registration, and the method-coverage string in MethodsTest. Pure reordering —
no behavior change.

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

blocks.validate requires no token or scopes
(https://docs.slack.dev/reference/methods/blocks.validate), so it should not
send an Authorization header. Model it like api.test: drop the token field from
BlocksValidateRequest (overriding getToken() to return null) and call it through
the tokenless postFormAndParseResponse path. The local BlocksTest now asserts the
request round-trips (the shared mock answers a tokenless call with not_authed);
end-to-end ok/errors[] behavior is covered by the remote blocks_Test.

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>