fix(pg-meta): tables.update and columns.update DO blocks fail when an identifier contains "$$"

## Summary `pgMeta.tables.update` (when `primary_keys` is supplied) and `pgMeta.columns.update` (the `is_unique: false` and `check: ...` paths) all build `DO $$ ... $$;` blocks whose body embeds `old.schema` / `old.name` / `old.table` via `ident()` inside strings that are then passed to `EXECUTE` or to `format()`. When any of those identifiers happens to contain the literal byte sequence `$$`, PostgreSQL's dollar-quote parser treats the first `$$` it sees in the body as the closing delimiter of the outer block, the body is parsed as truncated, and the statement fails with a `syntax error at or near "..."` error. This is the same class of bug as the recently-opened `pg-meta-table-privileges` (#49523), `pg-meta-column-privileges` (#49588), `pg-meta-roles` (#49600), `pg-meta-foreign-tables` (#49603), and `pg-meta-publications` (#49605) PRs — those five paths already use a collision-free `getDoBlockDelimiter(...)` helper. The same pattern still exists in two files: `pg-meta-tables.ts` (PK drop block) and `pg-meta-columns.ts` (UNIQUE drop block and CHECK replace block). ## Repro ```sql create table public."weird$$name" (id int primary key, val text); -- what pgMeta.tables.update({...name: 'weird$$name'...}, { primary_keys: [] }) -- generates on master today: do $$ declare r record; begin select conname into r from pg_constraint where contype = 'p' and conrelid = 1; if r is not null then execute 'ALTER TABLE public."weird$$name" DROP CONSTRAINT ' || quote_ident(r.conname); end if; end $$; -- ERROR: syntax error at or near "name" ``` The outer `$$` closes at the `$$` inside `"weird$$name"`, the body after that is parsed as the next statement, and the EXECUTE argument (which started with the literal text `ALTER TABLE public."weird$$name"`) is truncated at the first inner `$$`. PostgreSQL then chokes on the partial token. The same breakage applies to: - `pgMeta.columns.update(col, { is_unique: false })` for a column on a table whose name contains `$$` (the U…