fix: normalize column-level meta to config.meta for dbt 1.9+

[dtaniwaki]

Thanks for maintaining this project! I'd appreciate your review on this small fix.

Problem

In dbt 1.9+, column-level meta should be stored under config.meta rather than as a top-level meta property (see dbt deprecations). The previous logic in
_sync_doc_section was doing the opposite — it was merging config.meta into the top-level meta, which perpetuated the deprecated pattern.

Solution

When dbt v1.10+ is detected and a column has a top-level meta dict, normalize it by moving it into config.meta and removing the top-level meta key. This aligns the written YAML with dbt's recommended
structure going forward.

Before:

columns:
  - name: user_id
    meta:
      pii: true

After:

columns:
  - name: user_id
    config:
      meta:
        pii: true

The change also removes the now-unnecessary bidirectional merge logic, simplifying the code significantly.