feat: add GetContent + bump steemutil to v0.0.30

[ety001]

Summary

Add GetContent(author, permlink string) (*protocolapi.Content, error) wrapping condenser_api.get_content, for steemdb-sync's comment rescanner (Batch 5). Uses the single-object return pattern (like GetFollowCount): positional params [author, permlink], returns a pointer.

Bumps steemutil require v0.0.29 → v0.0.30, which provides the new Content / VoteState / Beneficiary types (steemutil #18, tag v0.0.30).

Why this depends on steemutil v0.0.30

The Content/VoteState types did not exist before. Critically, steemutil #18 corrected a spec error: the original requirement assumed the share_type fields were "always JSON strings", but live testing showed they are int/string-mixed (within one response, active_votes[].rshares has both a number 2125781185 and a string "221646137396"). Those fields use json.RawMessage in steemutil, so this SDK's tests deliberately exercise both forms.

Tests

go build ./... + go test ./... all green.

• TestGetContent — mock server returns a discussion with deliberately mixed share_type forms (top-level net_rshares as JSON string, total_vote_weight as JSON number; active_votes[0].rshares string vs [1].rshares number) to prove the json.RawMessage fields decode both forms steemd emits.
• TestGetContent_ParamsShape — asserts params is [author, permlink] (2-element positional array).
• GetContent added to the TestParamsShape_IsArrayNotObject table.

After merge

This SDK will need its own version bump (e.g. v0.0.30) so downstream consumers (steemdb-sync, etc.) can pick up GetContent.