Fix TimeRange __contains__ and add Timestamp __float__

[philipnbbc]

Details

This PR:

• Fixes TimeRange.__contains__ which wrongly returned False for TimeRange.from_str("[0:0_1:0)") in TimeRange.eternity() for example.
• Adds support for TimeRange arg to TimeRange.__contains__, which is equivalent to using contains_subrange.
• Adds a Timestamp.__float__ which simplifies and avoids typing issues when converting a TimeRange.length to a float.

Jira Issue

Jira URL: https://jira.dev.bbc.co.uk/browse/CLOUDFIT-5398

Related PRs

Where appropriate. Indicate order to be merged.

Links to external test runs/working deployment

Where appropriate, if separate to default CI run

Submitter PR Checks

(tick as appropriate)

• PR completes task/fixes bug
• Tests exercise code appropriately
• New features and API breaks are flagged in commit messages using magic strings
• Documentation updated (README, Confluence, Docstrings, API spec, Engineering Guide, etc.)
• Downstream repos have been checked for potential breaks & fixed as needed
• APIs/UIs/CLIs updated as required
• PR added to Jira Issue
• Follow-up stories added to Jira
• Any temporary code/configuration removed (e.g. test deployment environment, temporary commontooling branch)
• Any pins against pre-releases have been removed

Reviewer PR Checks

(tick as appropriate)

• PR completes task/fixes bug
• Tests exercise code appropriately
• Design makes sense, and fits with our current code base
• Code is easy to follow
• PR size is sensible
• Commit history is sensible and tidy

Info on Cloudfit PRs

• The checks above are guidelines. They don't all have to be ticked, but they should all have been considered.
• For more details on how to asses PRs, see: https://github.com/bbc/rd-apmm-docs-ways-of-working/blob/master/workflow/PRChecklist.md

[j616]

LGTM