Add comprehensive SWE Common position type tests

Issue: Sam-Bolling/CSAPI-Live-Testing#43

Added 27 new tests for previously untested SWE Common position extraction paths:

Vector Positions (5 tests):
- 2D and 3D Vector coordinate extraction
- Missing value handling (defaults to 0)
- Insufficient coordinates (< 2) returns null
- Missing coordinates array returns null

DataRecord Positions (12 tests):
- Field name variations: lat/latitude, lon/longitude/long, alt/altitude/h
- Altitude defaulting to 0 when missing
- Missing latitude or longitude returns null
- Empty fields array returns null
- Case-sensitive field name matching (documents limitation)
- Zero coordinates (0,0) as valid position

DataArray Trajectory Positions (6 tests):
- Last position extraction from multi-point trajectories
- 2D and 3D trajectory support
- Single-point trajectory handling
- Empty values array returns null
- Missing values property returns null
- Insufficient coordinates in last value returns null

Unsupported Position Types (4 tests):
- TextComponent returns null (geocoding not supported)
- XLink reference returns null (external fetch not supported)
- Null position returns null
- Undefined position returns null

Test Coverage Impact:
- Before: 54 tests in base.spec.ts
- After: 81 tests in base.spec.ts (+27 tests, +50% increase)
- Untested code: ~79 lines (Vector, DataRecord, DataArray, unsupported types)
- Now tested: All major SWE Common position extraction paths

All tests pass and validate correct behavior of the extractGeometry() function
for SWE Common position formats used in CSAPI server responses.

Author: Sam-Bolling