More PR feedback changes.

* More use of `anyhow`.
* Change `make_accessible` into `protect_linear_memory` to better demonstrate
  what it is used for; this will make the uffd implementation make a little
  more sense.
* Remove `create_memory_map` in favor of just creating the `Mmap` instances in
  the pooling allocator. This also removes the need for `MAP_NORESERVE` in the
  uffd implementation.
* Moar comments.
* Remove `BasePointerIterator` in favor of `impl Iterator`.
* The uffd implementation now only monitors linear memory pages and will only
  receive faults on pages that could potentially be accessible and never on a
  statically known guard page.
* Stop allocating memory or table pools if the maximum limit of the memory or
  table is 0.

crates/jit/src/code_memory.rs

@@ -25,7 +25,7 @@ struct CodeMemoryEntry {
 
 impl CodeMemoryEntry {
     fn with_capacity(cap: usize) -> Result<Self, String> {
-        let mmap = ManuallyDrop::new(Mmap::with_at_least(cap)?);
+        let mmap = ManuallyDrop::new(Mmap::with_at_least(cap).map_err(|e| e.to_string())?);
         let registry = ManuallyDrop::new(UnwindRegistry::new(mmap.as_ptr() as usize));
         Ok(Self {
             mmap,