add observation unsignedInt type example

[Ryanmtate]

Basic example for observation shows unsignedInt type is correctly parsed.

Generated RDF quads from the Observation:
<https://example.org/observation/12345> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://schema.org/Observation> .
<https://example.org/observation/12345> <https://schema.org/observationDate> "2023-03-15T14:30:00Z" .
<https://example.org/observation/12345> <https://schema.org/variableMeasured> "Temperature" .
<https://example.org/observation/12345> <https://schema.org/value> "22"^^<http://www.w3.org/2001/XMLSchema#unsignedInt> .
<https://example.org/observation/12345> <https://schema.org/unitCode> "CEL" .
<https://example.org/observation/12345> <https://schema.org/description> "Room temperature measurement" .

Generated RDF quads from the ObservationCollection:
<https://example.org/collections/temperature-log> <https://schema.org/name> "Daily Temperature Log" .
<https://example.org/observation/12345> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://schema.org/Observation> .
<https://example.org/observation/12345> <https://schema.org/observationDate> "2023-03-15T14:30:00Z" .
<https://example.org/observation/12345> <https://schema.org/variableMeasured> "Temperature" .
<https://example.org/observation/12345> <https://schema.org/value> "22"^^<http://www.w3.org/2001/XMLSchema#unsignedInt> .
<https://example.org/observation/12345> <https://schema.org/unitCode> "CEL" .
<https://example.org/observation/12345> <https://schema.org/description> "Room temperature measurement" .
<https://example.org/collections/temperature-log> <https://schema.org/hasPart> <https://example.org/observation/12345> .
<https://example.org/observation/12346> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://schema.org/Observation> .
<https://example.org/observation/12346> <https://schema.org/observationDate> "2023-03-15T15:30:00Z" .
<https://example.org/observation/12346> <https://schema.org/variableMeasured> "Temperature" .
<https://example.org/observation/12346> <https://schema.org/value> "23"^^<http://www.w3.org/2001/XMLSchema#unsignedInt> .
<https://example.org/observation/12346> <https://schema.org/unitCode> "CEL" .
<https://example.org/observation/12346> <https://schema.org/description> "Room temperature measurement after increasing thermostat" .
<https://example.org/collections/temperature-log> <https://schema.org/hasPart> <https://example.org/observation/12346> .