feat(cpp): add functions related to offset, tests related to consumer groups

[slbotbm]

Which issue does this PR address?

Closes #
Relates to #2100

Rationale

Additions of more functions and tests in the cpp sdk.

What changed?

• decouples delete_connection from logout_user function.
• adds logout_user, update_stream, store_consume_offset, get_consumer_offset, delete_consumer_offset, and flush_unsaved_buffer functions
• adds tests for join_consumer_group and leave_consumer_group, which were missing previously. Added cleanup related to consumer groups as well.
• All conversion code was moved into type_conversions.rs for ease of finding.
• Also added consumer and producer types for high-level api, and commented-out method signatures for the rest of the remaining functions in lib.rs

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

If AI tools were used, please answer:

1. Which tools? codex
2. Scope of usage? code generation, researcg
3. How did you verify the generated code works correctly? tested it, read through it
4. Can you explain every line of the code if asked? yes

[github-actions]

Thanks for the PR. It is labeled S-waiting-on-review and queued for review.

Slash commands (own line, regular comment) move it around the queue:

• /ready - back to S-waiting-on-review after addressing feedback
• /author - flip to S-waiting-on-author while you finish changes
• /request-review @user-or-team - request a reviewer

See CONTRIBUTING.md for details.