fix: make custom beacon chart stable in visreg

[hcopp]

What changed? Why?

This PR makes a line chart example stable so the data is the same each load.

Root cause (required for bugfixes)

This example was generating new random data each time and as a result was being flagged in visual regression tests.

UI changes

Before

Random data each load

After

Static sample data

Testing

How has it been tested?

• Unit tests
• Interaction tests
• Pseudo State tests
• Manual - Web
• Manual - Android (Emulator / Device)
• Manual - iOS (Emulator / Device)

Testing instructions

Illustrations/Icons Checklist

Required if this PR changes files under packages/illustrations/** or packages/icons/**

• verified visreg changes with Terran (include link to visreg run/approval)
• all illustration/icons names have been reviewed by Dom and/or Terran

Change management

type=routine
risk=low
impact=sev5

automerge=false

[cb-heimdall]

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✅ CODEOWNERS

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