fix(params): give a placeholder inside an INSERT VALUES call its slot

[tiagolauer]

Fixes #269.

The bug

Params<DB, 'insert into users (id, name) values (coalesce(?, 0), ?)'>   // [string]
Params<DB, 'insert into users (id, name) values (coalesce(@a, 0), @b)'> // [string]
Params<DB, 'insert into users (id, name) values (coalesce($1, 0), $2)'> // [unknown, string]

The README promises the opposite — "A placeholder inside a call is typed (lower($1), coalesce($1, 0))" — and it does work in WHERE.

The @ variant is the one that bites hardest, and it does it silently: the caller can only pass one value, resolveMixedParameters scans @a first and gives it that value, binds @b = null, and the INSERT succeeds having written into the wrong column.

The fix

MatchInsertValues runs IsPlaceholder on each VALUES entry as one token, and StripCallWrapper bails on any inner comma, so the placeholders inside the call never registered. (WHERE only works by accident of space-splitting, which isolates coalesce($1, as its own token.)

An entry that is not itself a placeholder now has its call's argument list split, and each argument is checked again. That is enough: a single-argument call around a placeholder (lower(?)) is something CleanScanToken already unwraps, so nesting keeps working. The type still comes from the matching entry in the INSERT column list.

Verification

tests/insert-values-call-params.test-d.ts, eight cases. Four red on master:

tests/insert-values-call-params.test-d.ts(18,3): error TS2344: Type 'false' does not satisfy the constraint 'true'.
tests/insert-values-call-params.test-d.ts(25,3): ...
tests/insert-values-call-params.test-d.ts(32,3): ...
tests/insert-values-call-params.test-d.ts(39,3): ...

• ?, @name and $n inside coalesce(x, 0) all reach [number, string]
• a nested coalesce(lower(@b), $$x$$) too, which also pins that a dollar-quoted body is not read as a placeholder

Controls: bare placeholders, a single-argument call, literals taking no slot, and the WHERE-clause form that already worked.

tsc --noEmit clean, 192 runtime tests pass, budget 192,807 (+321).