fix: correct naming of aggregated results when using variables

[ehrhart]

Using aggregates with a variable (e.g., { v: "?v$sum" }) would "incorrectly" generate SPARQL queries like: (SUM(?v) AS ?v). While technically accepted/ignored by Virtuoso, it causes errors with stricter engines like GraphDB.

The naming convention is now adjusted to generate unique variable names, such as (SUM(?v) AS ?v_sum). It was already the case when using expressions such as $schema:value$sum, but it didn't apply to variables. This commit fixes that behavior.

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✔ DBpedia list of cities (proto) ✔ DBpedia list of cities and regions (jsonld) ✔ DBpedia grunge bands ✔ DBpedia genres with bands ✔ Aggregates ✔ No lang tag ✔ Duplicate variable name ✔ List-required fieds ✔ Library limit (103ms) ─

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