fix(format): preserve dialect-specific SQL in MODEL/AUDIT/METRIC headers

[mday-io]

Description

#5864 fixed formatting corrupting SQLMesh's own header properties (on tsql, allow_partials TRUE was becoming the unparseable (1 = 1)) by no longer transpiling MODEL/AUDIT/METRIC headers at all.

That was too broad a fix: it also stopped transpiling the properties that are real warehouse SQL, like columns, audits, and physical_properties. So columns (ts DATETIME2(6)) would silently flatten to generic TIMESTAMP(6). On tsql this compounds across repeated formatting — DATETIME2 → TIMESTAMP → reparsed as ROWVERSION → VARBINARY — so two sqlmesh format passes could turn a datetime column into a binary one with no error.

This PR renders header properties individually instead of applying one blanket rule. Properties holding real warehouse SQL (columns, audits, physical_properties, macro properties, and expression fields nested inside kind like time_data_type/unique_key/time_column) render with the model's dialect. Properties that are SQLMesh's own semantics (allow_partials, description, scalar kind properties like forward_only) stay dialect-agnostic. Which bucket a property falls into is derived automatically from its field declaration, so the split stays correct as new properties are added, and a missed property fails safe — a keyword goes uncanonicalized rather than a user's SQL being corrupted.

Covers MODEL, AUDIT, and METRIC headers.

Test Plan

• test_format_model_expressions_meta_render_policy (parametrized over tsql/fabric) and test_format_audit_expressions_meta_render_policy, asserting columns, audits, physical_properties, and kind's nested expression properties keep their dialect-specific spelling while SQLMesh's own scalar properties stay dialect-agnostic.
• test_format_model_expressions_is_idempotent, parametrized over columns, audits, kind, physical_properties, SQLMesh-owned scalars, and macro properties, asserting a second sqlmesh format pass is a no-op.
• test_format_model_expressions_time_column_dialect — time_column's identifier quoting (e.g. tsql [end]) survives formatting instead of falling back to ANSI quoting.
• test_format_model_expressions_macro_property_comments_preserved_with_dialect — comments inside a macro header-property's arguments survive formatting on a dialect-bearing model, plus an idempotency check.
• test_format_model_expressions_kind_scalar_sibling_dialect — a kind block combining an expression property (time_column) with a boolean scalar sibling (forward_only) on tsql round-trips both correctly; asserts on the formatted string and round-trips through load_sql_based_model to confirm model.kind.forward_only is True survives (not just the string).
• pytest tests/core/test_dialect.py — 173 passed.
• ruff check on the changed files — clean.

Release Note

Fix: sqlmesh format corrupting warehouse-specific types in MODEL/AUDIT/METRIC headers

sqlmesh format on models with an explicit dialect (tsql, fabric, and others with dialect-specific type spellings) could silently rewrite warehouse-specific types in columns, audits, physical_properties, and kind-nested properties (e.g. time_data_type, time_column) to a generic spelling. For tsql specifically, this was compounding: DATETIME2 → TIMESTAMP → VARBINARY across two format runs — for an SCD Type 2 model's time_data_type, that silently turned the physical type of the valid_from/valid_to columns from a datetime into a binary type.

Header properties that hold SQLMesh's own semantics (allow_partials, description, kind name, boolean kind properties like forward_only, etc.) are unaffected and continue to render dialect-agnostically, so this only changes output for the subset of header properties that carry actual warehouse SQL.

Action for affected users: if you run sqlmesh format on tsql/fabric models with warehouse-specific types in columns, audits, physical_properties, or SCD kind blocks, re-run sqlmesh format after upgrading and review the diff — previously-corrupted types will be restored to their correct dialect-specific spelling.

Checklist

• I have run make style and fixed any issues
• I have added tests for my changes (if applicable)
• All existing tests pass (make fast-test)
• My commits are signed off (git commit -s) per the DCO