fix: ensure timestamp and isoTimestamp return current time instead of random values

[anusree-bruno]

Description

This PR addresses the issue where the timestamp and isoTimestamp functions were returning random values instead of the current time. The changes ensure that both functions now return the actual current time.

Closes #4631
Jira: https://usebruno.atlassian.net/browse/BRU-1131

Changes Made:

• Updated the timestamp function to return the current Unix timestamp in seconds.
• Updated the isoTimestamp function to return the current time in ISO format.
• Added tests to verify that both functions return current time values within a 2-second window.

Before:

After:

Contribution Checklist:

• The pull request only addresses one issue or adds one feature.
• The pull request does not introduce any breaking changes
• I have added screenshots or gifs to help explain the change if applicable.
• I have read the contribution guidelines.
• Create an issue and link to the pull request.

Note: Keeping the PR small and focused helps make it easier to review and merge. If you have multiple changes you want to make, please consider submitting them as separate pull requests.

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