[Temporary on v18.4.0 tag]: using tracing for theming debug

[philtweir]

Improving alignment of the debug within theming with the rest of atuin.

Originally, I had just added log as I was not sure how best to link in, but this uses tracing, which is present elsewhere.

As such, you can see theming-related logging by using:

ATUIN_LOG=1 atuin search -i

For example:

Unfortunately, it is a bit hard to read on top of an interactive prompt, so if there is a simple workaround I am missing, please say.

Originally, I was worried about theme debug interfering with other logging, but having a debug parameter may be redundant if tracing can give more control anyway - perhaps it should be removed?

Checks

• I am happy for maintainers to push small adjustments to this PR, to speed up the review cycle
• I have checked that there are no existing pull requests for the same thing

[ellie]

btw you can filter tracing by specifying the module, eg

ATUIN_LOG=atuin_client=debug

to set logs to debug, only for atuin_client