chore: align PL/pgSQL and CLI package versions with PG18 (18.0.0)

[pyramation]

Summary

Version-only bump so every package on the PG18 stack shares the 18.x major, making the PostgreSQL major obvious from the package version:

• plpgsql-parser, plpgsql-deparser, plpgsql-parse, pgsql-parse: 1.0.0 → 18.0.0
• @pgsql/cli: 2.0.0 → 18.0.0

No code changes; internal deps use workspace:* so no range updates needed. Intended to be published as 18.0.1 via the next lerna publish.

Link to Devin session: https://app.devin.ai/sessions/064ad193e1c040af8c145d55e07af9b8
Requested by: @pyramation

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