Implement write methods for PostgreSQLUnspecifiedBinaryProtocolValue

[daguimu]

Problem

PostgreSQLUnspecifiedBinaryProtocolValue.write() and getColumnLength() throw UnsupportedSQLOperationException, preventing unspecified-type values from being written through the PostgreSQL binary protocol path.

Root Cause

The write() and getColumnLength() methods were left as stubs throwing UnsupportedSQLOperationException when the class was initially created. This is one of the items tracked in #35830.

Fix

Implemented both methods following the same pattern as PostgreSQLStringBinaryProtocolValue:

• getColumnLength(): returns the byte length of value.toString() using the payload's charset, correctly handling multi-byte characters
• write(): writes the string representation via payload.writeStringEOF(value.toString()), which works for both plain String values and PostgreSQLTypeUnspecifiedSQLParameter instances (which delegate to their inner string via toString())

Removed the unused UnsupportedSQLOperationException import.

Tests Added

Change Point	Test
getColumnLength returns correct byte length	assertGetColumnLength — "val" → 3, PostgreSQLTypeUnspecifiedSQLParameter("test") → 4
getColumnLength handles multi-byte characters	assertGetColumnLengthWithMultiByteCharset — "中文" → 6 (UTF-8)
write outputs string bytes to payload	assertWrite — verifies "val" bytes written to ByteBuf
write works with PostgreSQLTypeUnspecifiedSQLParameter	assertWriteWithTypeUnspecifiedParameter — verifies "test" bytes written

Impact

Only affects the unspecified binary protocol value type in the PostgreSQL protocol module. Enables binary write support for unspecified-type columns. No changes to other protocol value implementations.

Partial fix for #35830

[daguimu]

Hi, I have just addressed the Spotless violations in a follow-up commit; CI should now pass. Would appreciate a review when someone has time. Thanks!