`INTERVAL` does not allow for sign (+/-) before the literal

[alancai98]

Description

• INTERVAL literals do not allow for a sign before the interval value
• Parsing is fine but bug is in the AST -> Plan conversion

To Reproduce

partiql ▶ INTERVAL '-10' YEAR (2);
e: [semantic] Unexpected failure encountered. Caused by: java.lang.IllegalStateException: Invalid interval string: '-10'.
java.lang.IllegalStateException: Invalid interval string: '-10'
        at org.partiql.planner.internal.util.IntervalUtils.parseIntervalSingle(IntervalUtils.kt:48)
        at org.partiql.planner.internal.util.IntervalUtils.parseInterval$partiql_planner(IntervalUtils.kt:21)

Expected Behavior

Expect to be able to parse negative interval literal values/.

Additional Context

• Java version: 17
• PartiQL version: 1.2.3-SNAPSHOT