[FR] - Tooling for slot - unixtime conversion

[nielstron]

Internal/External
External

Area
Plutus

Describe the feature you'd like
There is currently only external tooling for converting between unixtime and slot time. This is a nuisance because

• Plutus works with Unix timestamps
• building a transaction with the CLI expects invalid-hereafter and invalid-before in slots
• native scripts work with slots

A simple command to convert between the two, given the network, would help a lot.

Describe alternatives you've considered
An alternative is adding a invalid-hereafter-unixtimestamp-ish flag to transaction build, but it is not nearly as widely applicable
(for example tools may want to check what unix time a specific slot returned by the CLI corresponds to)

Additional context / screenshots
This would also be useful to be able to convert between native scripts and plutus scripts, see this comment: cardano-foundation/CIPs#392 (comment)

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 120 days.

[nielstron]

This is still relevant to me

[newhoggy]

Is there a need to query past the horizon on the understanding that such queries may return incorrect results past a hard fork?