sparql_query: accented characters in string literals are corrupted before HTTP transmission

[aborruso]

When using sparql_query to query the Wikidata SPARQL endpoint with string literals containing accented characters (e.g. "Nestlé"@en), the query returns 0 results even though the entity exists with that exact label.

Root cause

The é character (U+00E9, UTF-8: C3 A9) appears to be corrupted or incorrectly encoded when the tool serializes the SPARQL query string into the HTTP request body. Wikidata confirms the label is stored as precomposed é (U+00E9).

Steps to reproduce

Run the following query against https://query.wikidata.org/sparql:

```sparql
SELECT ?item WHERE {
?item rdfs:label "Nestlé"@en .
}
LIMIT 5
```

Returns 0 results. The entity Q160746 has English label "Nestlé" and should match.

Workaround

Use wikibase:mwapi EntitySearch service instead of rdfs:label exact match:

```sparql
SELECT ?item ?itemLabel WHERE {
SERVICE wikibase:mwapi {
bd:serviceParam wikibase:endpoint "www.wikidata.org" ;
wikibase:api "EntitySearch" ;
wikibase:limit "5" ;
mwapi:search "Nestle" ;
mwapi:language "fr" .
?item wikibase:apiOutputItem mwapi:item .
}
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" . }
}
```

Note: this only works for Wikidata and requires omitting the accent in the search term, which is a poor workaround.

Expected behavior

UTF-8 string literals in SPARQL queries should be transmitted as-is, without normalization or corruption of non-ASCII characters.