feat(format): add the expanded statement layout

[edjubert]

What

A new layout option:

Option	Default	Values
layout	"fit"	"fit", "expanded"

• fit - today's behaviour: a clause breaks only when the line would exceed lineWidth.
• expanded - SELECT target lists, joins and INSERT column lists always break, whatever the line width.

-- input
SELECT t.a, t.b FROM s.t WHERE t.c = 1 GROUP BY t.a ORDER BY t.a;

-- layout=expanded
select
	t.a,
	t.b
from
	s.t
where
	t.c = 1
group by t.a
order by t.a;

Joins each get their own line:

-- input: SELECT a FROM a LEFT JOIN b ON b.a = a.a JOIN c ON c.a = a.a;
select
	a
from
	a
	left outer join b on b.a = a.a
	inner join c on c.a = a.a;

INSERT with a CTE:

insert into t.x (
	a,
	b
)
with
c
as (
	select
		1 as a,
		2 as b
	from
		t.y
)
select
	c.a,
	c.b
from
	c;

Why

With fit, whether a query is one line or ten depends on how long its identifiers happen to be.
Two queries with the same shape can be formatted differently, and adding a column can reflow an entire statement.
expanded makes the printed shape a function of the query structure alone, which keeps diffs minimal and reviewable - the property people want from a formatter in a versioned SQL repository.

Implementation

A clause_break(e) helper in nodes/mod.rs emits a hard break under expanded and a soft one under fit.
select_stmt.rs, join_expr.rs and insert_stmt.rs call it where they previously emitted a soft line.
No new renderer state.

Wiring: pgls_configuration (--layout), pgls_workspace settings, docs/features/formatting.md, docs/schema.json.

Tests

Three new fixtures snapshotted at widths 80 and 100 - identical at both widths, which is exactly the property expanded promises.

The two preparatory commits

The first two commits of this PR are shared, byte for byte, with the three other formatter-option PRs open alongside it:

• #795 — commaStyle / logicalOperatorPlacement
• #796 — clauseBodyStyle / isolateSemicolon
• #798 — castStyle

The shared commits are:

• test(pretty-print): allow per-fixture format configuration
• refactor(pretty-print): thread the format config into the emitter

They are carried in each PR so every option remains independently reviewable and mergeable.
Whichever PR lands first, I will rebase the other three to remove the duplicate commits.

Merge them in whatever order suits you; nothing here depends on the others.