fix(checks): descendants JSONPath always returns a list

[davidberenstein1957]

Summary

• Same fix as fix(checks): descendants JSONPath returns scalar vs list depending on match count #2634 by @Qalipso: treat JSONPath Descendants (..) as a list-expression so resolve() always returns a list (not a bare scalar when there is exactly one match).
• Fixes lint on a same-repo branch: fork fix(checks): descendants JSONPath returns scalar vs list depending on match count #2634 fails check-format because README code blocks need the current ruff formatter and fork PRs cannot receive the auto-format push.
• Also applies the review suggestion on fix(checks): descendants JSONPath returns scalar vs list depending on match count #2634 (drop the long inline comment) and a pre-existing reportInvalidTypeForm ignore for MISSING (same pattern as runner.py) so pre-commit basedpyright passes.

Fixes #2633.
Supersedes #2634.

Test plan

• make test-unit PACKAGE=giskard-checks → 761 passed, 4 skipped
• CI lint + unit tests on this PR
• Confirm Equals(key="trace..ctx", match="any") is stable for one vs many matches