I initially planned to implement a scanner-less parser, but however, the
complexity was unnecessary and the performance improvements were marginal.
With increasing language complexity, such a pipeline would become even more
complex and hence, I re-implemented the parser with a traditional "proven"
lexer-parser pipeline. More performance improvements are possible, and I
will add them ahead.
In an earlier commit we marked `as_slice` as safe to call, stating
that only construction is unsafe. However, that is incorrect. The
ctor of `UnsafeSlice` does nothing unsafe, unless we make as_slice
safe. However, since the type is not bounded to any lifetime,
making `as_slice` safe to call assumes a very "rarely true"
safety contract: that the pointers are valid throughout the
execution of the program, id est they are static.
However, that assumption is entirely incorrect for our use case,
hence I'm marking this as `unsafe` again.
For some spurious reason, the tree test is failing on the M1
builder; so we'll hack around by ignoring the test when run
on the M1 CI. Note to self: the test runs successfully on
a physical M1 machine so it is likely that this is a problem
with the runner.