kernel(lectionary): fix round 1 -- load never raises

Sexplib.Sexp.load_sexp raises bare Failure for several malformed inputs
(unterminated list/string, empty file, more than one sexp) rather than
Sexplib.Sexp.Parse_error, so those cases escaped Lectionary.load as an
uncaught exception -- breaking the .mli's own promise and the kernel's
never-raises-on-fallible-construction constraint. Mirrors the catch-all
already present in Layer.load and Overlay.load, plus a second catch-all
on the t_of_sexp branch for defence in depth.

Adds test_load_never_raises, covering all of the above plus a missing
file, using Filename.temp_file rather than a hardcoded path. Verified the
new test fails against the pre-fix load (uncaught Failure) and passes
against the fix.

0 files changed, 0 insertions, 0 deletions