Bring Sql\Ddl to Mago compliance

[simon-mundy]

Takes Sql\Ddl out of the lint baseline entirely and leaves 3 of its 62 analyzer findings, and fixes a TypeError in getRawState() along the way.

Stacked on #230 (Predicate), which is stacked on #229 (baseline refresh). Only the last two commits are new here.

Bug fixed

AlterTable::getRawState() and CreateTable::getRawState() declared array|string. Asking for the table of a statement built with a TableIdentifier therefore threw:

(new AlterTable(new TableIdentifier('t', 's')))->getRawState(AlterTable::TABLE);
// TypeError: Return value must be of type array|string, PhpDb\Sql\TableIdentifier returned

Both now declare TableIdentifier as well, and describe the raw state with a RawState shape.

Cleanup

• The DDL process*() methods take a PlatformInterface, not ?PlatformInterface = null. buildSqlString() always passes one, and the phpdb-mysql decorators already cast it to non-null. Their ?PlatformInterface overrides stay compatible, because a wider parameter type in a child is allowed.
• CreateTable::processCombinedby() returns an empty parameter list rather than reading the separator back out of $specifications. processStatementEnd() drops the platform parameter it never used.
• AlterTable builds its column, constraint and index lists with array_map instead of five hand-written loops. This clears its kan-defect.
• The column constructors type $default as the values setDefault() accepts, where they used to take mixed, and Column::$default now starts as null. Constructors are exempt from signature compatibility, so subclasses are unaffected.
• ForeignKey::$referenceSpecification is typed as the two-part shape getExpressionData() reads.
• AbstractPrecisionColumn::getLengthExpression() is a single match, which clears its halstead finding.
• Every class and interface in the component is tagged @api, not made final, as in Bring Sql\Predicate to full Mago compliance #230.
• In mago.toml, AlterTable and CreateTable join the too-many-methods exclusions as fluent builders. ForeignKey and AbstractPrecisionColumn are excluded from excessive-parameter-list: their public constructors take one argument per part of the definition they model.

Left for the DML pass

Three findings remain, one per processTable(). They trace back to AbstractSql::resolveTable() declaring string|array|null. Only Select's override returns an array; it reuses the name for a different [table, fromTable] shape. Fixing that is a Select change, so it belongs with the DML PR.

Result

	Before (#230)	After
Lint baseline (issues)	222	216
Analyzer baseline (issues)	697	638
src/Sql/Ddl in either baseline	68	3
PHPUnit	2154 tests	2156 tests

Line and method coverage of src/Sql/Ddl is 100%. Infection reports 100% covered-code MSI: 287 killed and 5 caught by static analysis.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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The merge-base changed after approval.