PERF: delay preset sync until tab completion is accessed

[tangkong]

Description

Delays preset file reading until tab-completion has been attempted. Stashes this information on the device instance itself. This is not the default behavior, and you must opt into this by supplying the optional argument defer_loading to setup_presets_paths

Motivation and Context

Presets have taken a very long time to load recently, and the first place to look is often file i/o. This delays this as long as possible while attempting to preserve the behavior hutch scientists use: tab completion.

This has also been made optional. Both setup_presets_paths and Presets.sync() now take an optional defer_loading argument, that if true will skip the preset data loading step

In a nutshell:

• the device instance tracks whether a tab-completion has been attempted
  • if it hasn't, it skips any Presets.sync() method call
  • if it has, run Presets.sync() with defer_loading=False (the default)

How Has This Been Tested?

Tests pass

Tested interactively through hutch-python, loading some subset of 559 xcs presets

• this PR: 7.53s (0.01345s / preset)
• current master: 16.21s (0.0289s / preset)

There's some variation but I'm not going to do a battery of tests here

Why isn't this just 0 s?

There's still some path access going on in hutch-python, it's just stopping short of actually opening the presets file.

Where Has This Been Documented?

This PR, a stray comment

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