Proposal: Format SQL around standalone psql commands

[arnodirlam]

A proposal for #83: format PostgreSQL between standalone psql commands while preserving the command lines and arguments.

With parser: "psql" and otherwise default options:

Before:

\set ON_ERROR_STOP on
\if :ready
select id,name from widgets where active=true
\gset widget_
\else
  \echo Not ready
  \quit
\endif

After:

\set ON_ERROR_STOP on
\if :ready
SELECT id, name FROM widgets WHERE active = TRUE
\gset widget_
\else
  \echo Not ready
  \quit
\endif

The separate parser makes this opt-in. It never adds final semicolons, even with sqlFinalSemicolon: true, since doing so before \gset could execute the query twice.

This deliberately starts small: unparseable SQL fragments stay as written, including unsupported psql variable interpolation and inline commands. Scripts mentioning COPY remain untouched to protect inline data; that conservative check also catches mentions in comments and strings.

I'd appreciate your thoughts on whether this belongs here or in the underlying parser, and whether preserving unsupported fragments is the right behavior. Feel free to close this PR if it isn't wanted.

[nene]

As explained in #83, I'm rejecting this. The parsing code should live inside a parser.

Also, I'd like to avoid a regex-based parsing approach. I'd really prefer having a proper grammar defined for it.

Additional thing to note is the handling of COPY. This is really a feature missing in the PostgreSQL parser.