fix: render Jinja blocks before splitting on semicolons (#2650)

[sfc-gh-moczko]

Summary

• Fixes SNOW-2397013: Jinja IF-statements are not interpreted correctly #2650: Jinja block statements ({% if %}, {% for %}, etc.) containing semicolons were broken because split_statements() splits on ; before Jinja rendering, producing invalid template fragments.
• Moves Jinja rendering to a pre-render step on the whole content before split_statements(), while legacy (&{ }) and standard (<% %>) syntax continues to render per-statement (they are variable-only, no blocks).
• Adds 7 new tests covering: if-blocks, for-loops, if/else, mixed Jinja+standard syntax, false conditions, file-based input, and undefined variable errors.

Root Cause

The SQL execution pipeline called split_statements() then per-statement template rendering. Since split_statements is unaware of Jinja block syntax, a query like:

{% if var == 'Jinja' %}select 1;{% endif %}

was split into two broken fragments:

1. {% if var == 'Jinja' %}select 1; -- unclosed if block --> TemplateSyntaxError
2. {% endif %} -- orphaned endif --> TemplateSyntaxError

Fix

Jinja block rendering now happens on the whole content before splitting. The per-statement pipeline still handles legacy/standard variable substitution (which never had block syntax). This is safe because Jinja {{ }}/{% %} syntax is orthogonal to <% %>/&{ } -- rendering one leaves the other untouched.

Changes

File	Change
statement_reader.py	Add pre_render parameter to query_reader() and files_reader()
manager.py	Split Jinja into pre-render step (whole content) + per-statement step (legacy/standard only)
tests/sql/test_sql.py	Add 7 test cases for Jinja block scenarios

Test plan

• Reproduction test passes
• For-loop test produces 3 statements
• If/else test selects correct branch
• Mixed Jinja + standard syntax works
• False condition raises CliArgumentError (no statements to execute)
• File-based Jinja blocks via -f flag work
• Undefined variable in block raises clear error
• All 83 tests in test_sql.py pass (including 10 existing parametrized syntax config tests)
• All 33 test_statement_reader.py tests pass
• All pre-commit hooks pass (ruff, black, mypy, codespell)
• Live Snowflake smoke test: 3 scenarios pass end-to-end