Formal states in tables

[MichaelTimbert]

Purpose

Introduce a formal state column to the test_results table, replacing the implicit state inference from the progress integer with explicit, well-defined lifecycle states.

Context

#960

Previously, the state of a test was derived from the progress value (0 = waiting, 1-99 = running, 100 = completed). This made it impossible to distinguish between different terminal states (e.g., completed normally vs. cancelled vs. crashed). This PR adds a proper state column with five formal states.

Changes

• Database schema (MySQL, PostgreSQL, SQLite): Added state VARCHAR(20) NOT NULL DEFAULT "waiting" column with a CHECK constraint limiting values to waiting, running, completed, cancelled, crashed.

• State constants (DB.pm): Lowercased existing constants (WAITING → waiting, RUNNING → running, COMPLETED → completed) and added two new ones: $TEST_CANCELLED and $TEST_CRASHED.

How to test this PR

• Run the existing test suite to verify all state transitions work correctly.
• Verify database schema creation includes the new state column and CHECK constraint on all three backends (MySQL, PostgreSQL, SQLite).
• Confirm that cancelled and crashed tests are properly distinguished in the state column.