No colour differentiation for actual/expected values in test failure output

[mtharrison]

When a test fails due to an expectation mismatch, the actual and expected values are displayed without colour differentiation, making them hard to distinguish at a glance.

Current behaviour

Failure output shows:
```
actual expected

'aaba'

Expected 'aa' to equal specified value: 'ba'
```
All text appears in the same colour.

Suggested behaviour

Apply colour coding to differentiate:

• Actual value (e.g., red)
• Expected value (e.g., green)

This should apply to:

1. The inline failure message in the editor
2. The tooltip next to the test name

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Feedback from Kevin Paxton