Fix pipe text-like DATE conversion

[Caideyipi]

Description

• Parse non-numeric TEXT/STRING/BLOB values with datetime syntax when converting to DATE in pipe receiver conversion.
• Keep numeric strings constrained to valid DATE integers and fall back to 1970-01-01 on invalid values.
• Add focused converter coverage and include the datetime sample in tree/table pipe type conversion IT data.

Tests

• mvn -Ddevelocity.off=true -pl iotdb-core/datanode,integration-test -P with-integration-tests spotless:apply
• mvn -Ddevelocity.off=true -pl iotdb-core/datanode -am -Dtest=ValueConverterTest -DfailIfNoTests=false -Dsurefire.failIfNoSpecifiedTests=false test