[Misc] Bump ray from 2.48.0 to 2.55.1

[knwgo]

PR Description

Bump ray from 2.48.0 to 2.55.1 in requirements.txt.

Context

In local testing, ray==2.48.0 fails to start the Ray cluster, while ray==2.55.1 works as expected. This PR pins to the verified-working version to unblock local development for contributors hitting the same issue.

2.55.1 was identified empirically as a known-good version (not a targeted fix for a specific root cause).

Related issue

May partially address #331 — the Ray version bump resolves the cluster startup failure observed locally, which appears to overlap with symptoms reported there. It is not a complete fix for #331; other aspects of that issue may still require follow-up.

Scope

• Single-line version bump in requirements.txt
• No code logic changes
• No test changes (deps-only)

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Checklist (Required)

• All code changes pass the pre-commit checks.
• Commits are signed off using git commit -s.
• The PR title is properly classified (see below).

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PR Type

[Misc] — dependency version bump.

Refs #331