Reduce startup time

[Thylane]

Fix #39. The change in startup time is shown in the figure below (recorded by exampleVault):

• left: load all languages at once → slow startup
• right: load on demand → starts faster, functions as usual

References:

• https://shiki.style/guide/install#usage
• https://expressive-code.com/key-features/syntax-highlighting/#langs

Note:

• For on-demand loading, async / await is added to the code that requires highlighter instance this.shiki to load language. Not sure if it will have any impact.
• In the updateWidgets function, the steps of building decorations are moved outside syntaxTree.iterate.

[acrogenesis]

this is cool

[mProjectsCode]

LGTM
Sorry, I forgot to rereview this PR.

[mProjectsCode]

I noticed after merging that eslint and prettier aren't happy. Please run the bun run check command before submitting a PR next time.

[Thylane]

I noticed after merging that eslint and prettier aren't happy. Please run the bun run check command before submitting a PR next time.

I ran bun run check and it was complaining about code style in almost all files. (Why?)
I accepted its suggestion to "Run Prettier with --write to fix" and... I don't like the format it imposes. (What now..)