`run_sql` with `no_transaction: true` mis-splits dollar-quoted ($$) PL/pgSQL blocks

### Version Information

Server Version: v2.48.5
CLI Version (for CLI related issue): n/a

### Environment

OSS

### What is the current behaviour?

When `run_sql` is called with `no_transaction: true`, the server splits the SQL into individual statements via [`splitSQLStatements`](https://github.com/hasura/graphql-engine/blob/417c174c0ac3c80dafe6e8f9e8ac39d868334724/server/src-lib/Hasura/Backends/Postgres/DDL/RunSQL.hs#L277). That splitter mis-handles bare `$$` dollar-quoting: it represents the empty tag internally as the single character "$", and its closing-delimiter check is a prefix match against that tag. As a result, any lone $ inside the body (e.g. a $ regex end-anchor in a string literal like `'^foo$'`) is mistaken for the closing `$$`. The parser then falls out of dollar-quote mode and treats the next `;` as a statement separator, slicing a single `DO $$ … $$;` / `CREATE FUNCTION … $$;` block into invalid fragments. Postgres then rejects the fragment with a syntax error.

This only happens with `no_transaction: true`; the default path sends the whole body in one call and is unaffected. Named dollar-quote tags ($tag$ … $tag$) are also unaffected.

The relevant code is at https://github.com/hasura/graphql-engine/blob/v2.48.5/server/src-lib/Hasura/Backends/Postgres/DDL/RunSQL.hs#L302-L335

### What is the expected behaviour?

No syntax error when running SQL that contains `$$` in no_transaction mode.

### How to reproduce the issue?

1. Call `run_sql` with `DO $$ BEGIN IF 'x' ~ '^x$' THEN NULL; END IF; END $$;` and `no_transaction: true`
2. Notice that it fails with Postgres syntax error
3. Run the same SQL, but without `no_transaction: true`.
4. Notice that it succeeds

### Screenshots or Screencast

### Please provide any traces or logs that could help here.

### Any possible solutions/workarounds you're aware of?

Use named dollar-quote tags (`$foo$`) instead of `$$`. Or don't use no_transaction.

### Keywords

Start in server/src-lib/Hasura/Backends/Postgres/DDL/RunSQL.hs, especially splitSQLStatements around lines 302-335. Reproduce the issue through run_sql with no_transaction: true using the provided DO $$ example, then verify that bare dollar-quoted blocks containing a lone $ remain one statement and execute without a syntax error, while named tags continue to work.

Written by the indexing model from the issue text.