Stream mode complete

[merv1n34k]

Hey @let-def!

I have rebased your changes on top of the main. Few things added after #130:

1. Bug fix

editor_notify_lookup in editor.c has a switch with no break statements — every (lookup-file ...) notification falls through to abort() and crashes texpresso.

Fix: add break after each case. 3 lines change.

2. Feature: (pause) / (resume)

In -stream mode, texpresso starts compiling immediately, before the editor has a chance to push the root file. The engine fails, the editor sends register + open, and the engine restarts. With multiple files this means several wasted restarts at startup.

(pause) lets the editor freeze the engine while priming the VFS:

launch -stream root.tex
(pause)
(register "root.tex")
(open "root.tex" ...)
(resume)

The engine then steps once with everything already in place. Works in both sexp and JSON. Backward compatible — clients that never pause behave identically.

Implementation: new EDIT_PAUSE / EDIT_RESUME commands, paused flag on persistent_state, guards on every engine_step call site. Test script included (make test-pause-resume).

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Seems this is the last bit, and I could finally move towards stream mode wiring to the texpresso.vim (texpresso.nvim) and my other project.

[merv1n34k]

UPD: bring back previous fix from #125 for interpret_open: relative_path() was called unconditionally, mangling relative paths so (open ...) from the editor never matched the deferred query target. Guard behind path[0] == '/' to mirror what interpret_register already does.

And also update test-register to lookup-file instead of request-file (target no longer exist as we removed it).

[merv1n34k]

On top of that, also replaced legacy test-request-file with test-lookup-file, updated all test to make them reproducible and deterministic and added 3 new test targets to CI.