Fixing imprecise TPR_TICK_NS constant

[KaushikMalapati]

Description

Changing TPR_TICK_NS from 5.384 to 70/13. 5.384 is imprecise enough to cause large errors in _get_delay used by TprMotor.readback.get() and TprTrigger.ns_delay.get().

Motivation and Context

#1302

How Has This Been Tested?

Interactively (The error was due to a misspelling)

Where Has This Been Documented?

Pre-release notes

Pre-merge checklist

• Code works interactively
• Code contains descriptive docstrings, including context and API
• New/changed functions and methods are covered in the test suite where possible
• Test suite passes locally
• Test suite passes on GitHub Actions
• Ran docs/pre-release-notes.sh and created a pre-release documentation page
• Pre-release docs include context, functional descriptions, and contributors as appropriate

[slactjohnson]

The only comment I have here is that it would be good to include a comment describing this strange fraction and what the approximate value is.

[slactjohnson]

Thank you for adding comments. LGTM.