[GH-3200] Serialize empty Geography LineStrings as valid WKB

[jiayuasu]

Did you read the Contributor Guide?

• Yes, I have read the Contributor Rules and Contributor Development Guide.

Is this PR related to a ticket?

• Yes, and the PR name follows the format [GH-XXX] my subject. Closes [BUG]: Empty Geography LineStrings produce malformed WKB #3200.

What changes were proposed in this PR?

• Write the required zero coordinate count when serializing an empty SinglePolylineGeography.
• Produce valid LINESTRING EMPTY WKB instead of a header-only, malformed byte sequence.
• Allow WKBGeography.fromS2Geography() to round-trip an empty LineString through JTS while preserving its SRID.

The malformed WKB was discovered while reviewing #3195. This PR isolates the pre-existing serialization defect from the ST_MakeLine feature. It does not define the separate behavior for ST_MakeLine(EMPTY, non-empty), which is tracked by #3202.

How was this patch tested?

• Full common module suite: 1,181 tests, 0 failures.
• Added an exact-WKB assertion for 010200000000000000.
• Added WKB-to-S2 and S2-to-WKB-to-JTS empty LineString round-trip coverage.
• Formatting and commit hooks passed.

Did this PR include necessary documentation updates?

• No. This corrects malformed internal serialization without changing the public API.

[jiayuasu]

Closing as superseded by #3195. The merged implementation now writes empty geography LineStrings as valid zero-coordinate WKB and also handles S2 singleton polylines by emitting an OGC-valid two-coordinate LineString, with round-trip coverage.