Fix macOS compatibility in tools/log.sh

[Kunal241207]

Summary

tools/log.sh used GNU-specific flags that are not available on macOS.

This change makes the script portable by:

• Replacing date --rfc-email with a helper that falls back to a compatible date format when the flag is unavailable.
• Replacing tee --append with the portable tee -a.

The behavior of the script remains the same, but it now works correctly on macOS systems.

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Checklist:

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[PranjalManhgaye]

@Kunal241207 nice fix. two quick questions: (1) Was using date -u in the fallback intentional? on linux we get local time, so i was wondering if we’d want the same on macOS , (may be removing that -u) (2) One “Started on:” has two spaces after the colon and the other has one—was that on purpose? Just curious. thanks

[Kunal241207]

@PranjalManhgaye Good catch, thanks!

1. The -u wasn’t intentional. You're right that date --rfc-email uses local time, so removing -u makes the fallback match the original behavior better.
2. The spacing difference wasn’t intentional either. I’ll normalize it to a single space.

I've pushed the update.