Standardize source-level with('multilabel') to single quotes

[GumpacG]

Summary

The source-level with("multilabel") / with("singlelabel") clause was rendered
with double quotes in the GremlinLang output of every GLV, while all other string
arguments render with single quotes. This aligns it to single quotes so GremlinLang
output is internally consistent.

Before / after

# before
g.with("multilabel").V().elementMap()
# after
g.with('multilabel').V().elementMap()

Changes

• Updated the canonical rendering in all 5 GLVs (Java, Go, JavaScript, .NET, Python).
  Go, JavaScript, and .NET each render this clause in two places (GremlinLang and
  GraphTraversalSource); both were updated.
• Added a GremlinLang unit test per GLV asserting the single-quote output.

Assisted-by: Kiro:claude-opus-4.8

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.39%. Comparing base (a28cd1f) to head (c4e0956).
⚠️ Report is 277 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3521      +/-   ##
============================================
+ Coverage     76.35%   76.39%   +0.03%     
- Complexity    13424    14265     +841     
============================================
  Files          1012     1036      +24     
  Lines         60341    64527    +4186     
  Branches       7075     7650     +575     
============================================
+ Hits          46076    49296    +3220     
- Misses        11548    12140     +592     
- Partials       2717     3091     +374     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.