CHORE: Update readme to reflect recent migration to tsdown.

[s-petey]

Fixes #
Reflect tsdown migration in the readme as the bundler used.

Description

No new dependencies, a simple readme update.

Type of change

Please mark relevant options with an x in the brackets.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Algorithm update - updates algorithm documentation/questions/answers etc.
• Other (please describe): -- Small readme update.

How Has This Been Tested?

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• Integration tests
• Unit tests
• Manual tests
• No tests required

Reviewer checklist

Mark everything that needs to be checked before merging the PR.

• Check if the UI is working as expected and is satisfactory
• Check if the code is well documented
• Check if the behavior is what is expected
• Check if the code is well tested
• Check if the code is readable and well formatted
• Additional checks (document below if any)

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commit: 06c2035

[AlemTuzlak]

@s-petey thank you! mind just running the linter?