chore: add ryol8888 to SIG-converters Contributors and Approvers

[andife]

Summary

Adds ryol8888 (GitHub handle for their org membership; commits/PRs land under dongryeolle — same person) to CONTRIBUTORS:

• As a Contributor — this is a backfill. ryol8888 is already an active member of the sig-converters GitHub team, but was missing from this file entirely.
• As an Approver — per the process in this file's header, submitted with justification below. @xadupre and @kevinch-nv (SIG-converters chairs) were notified directly beforehand, per the approver-sponsorship requirement; this PR is the formal request for their review.

Justification

Sustained contributions to onnx/tensorflow-onnx, October 2025 – August 2026:

• #2473 — derive opset→IR version map from ONNX's release table, CI for opset 19-22 & ONNX 1.21/1.22
• #2474 — fix numpy 2.0-removed aliases
• #2475 — untangle protobuf/numpy test pinning
• #2471 — non-blocking TFLite builtin coverage guard (CI tooling)
• #2414 — transpose optimizer: support NHWC→NCHW through multi-output Split nodes

Also holds an open tracking issue (#2472) for broader ONNX-version sync work, so this reflects sustained engagement (~10 months) rather than a one-off contribution.

Review engagement: on #2468 (another contributor's PR tackling the same opset/IR problem), they caught a design issue and proposed a better approach, backed by empirical onnxruntime compatibility testing — solid enough that the original author closed their PR in favor of this one.

Notes for reviewers

• Most of the track record so far is authoring rather than reviewing PRs/issues — #2468 is the clearest example of engaging with someone else's work. This has already been communicated directly as an expectation to keep building on going forward.
• Comfortably clears the 3-month active-approver-eligibility bar.
• Two GitHub accounts are involved: org/team membership is under ryol8888, while all linked contributions are authored under dongryeolle — confirmed to be the same person via profile.