[bugfix] preserve special characters in promql queries

[Hanabi9248]

What's changed?

PromQL expressions are inserted directly into query parameters, leaving + and & unescaped. The server decodes addition operators and regex quantifiers as spaces, and an ampersand in a label value splits the expression into another parameter. For example, sum(up{job=~"api.+",label="a&b=50%"}) + 1 arrives truncated and altered.

Encode the expression as a URI template value in execute and both instant and range query requests. The regression captures the URI from each actual executor path and checks the server-decoded parameters, including the range bounds and step.

Validation on Windows with Java 25: all 10 query-executor tests pass, including the three new regressions that fail before the fix. Maven Checkstyle and git diff --check pass. The full warehouse suite and a live Prometheus server were not run.

Checklist

• I have read the contributing guide.
• The regression test documents the affected query and expected behavior.
• Added the necessary unit tests; all query-executor tests pass.

Add or update API

No API changes.