[46] parallel filesystem convention example

[TomStrepsil]

Issue

resolves #46

Details

Provide an example, within the expressjs harness, demonstrating a filesystem convention (enabled by #54) whereby features exist as parallel filesystems that "patch" modules on the mainline.

Include variations of:

• files containing only constants
• css modules
• redux slices
  • all of the above use an objectProxyTogglePoint using an Proxy to retarget access to appropriate variations at access-time
• react components
  • uses the default toggle point from the react-pointcuts package
• redux reducer maps
  • a basic higher-order function toggle point, reliant on a getReducerMap factory function as the control

...to demonstrate potential toggle point configuration for these. The README.md for the example explains further.

To demonstrate the use of valtio (previously only mentioned in passing in the features package docs), this is used to make a reactive features store on the browser.

Scout Rule

• convert deprecated unstable_config_lookup_from_file to v10_config_lookup_from_file now that its stable awaiting next major version.
• upgrade eslint to 9.38.0
• change the "config example" to use "I am" rather than "I'm" after a weird playwright failure with the "large config" example that no longer rendered the html entity for the apostrophe properly. Not gonna fight it.
• update @playwright/test to 1.56.0

Screenshots

3x button click:

change to "feature 1":

2x button click:

change to "feature 2":

click "⛓️‍💥"

change to "feature 3":

4x button click:

change to "feature 4":

reload, with "feature2" header, then change to "feature 5":

CheckList

• PR starts with [ISSUE_ID].
• Has been tested (where required) before merge to main.