Specialize Enumerable#max and Enumerable#min for Range #4560

[lopopolo]

This patch prevents a hang for pathalogical (large) Ranges when computing max and min.

Range inherits its implementation of max and min from Enumerable. Enumerable implements max and min by calling each. For Range objects, this is unnecessary since we know the max and the min by the end and begin attributes.

It is also very slow. This code hangs unnecessarily:

(0..2**32).max
# ... hang
(0..2**32).min
# ... hang

This patch overrides max and min after including enumerable to yield based on the begin and end methods.

Upstream PR is mruby/mruby#4560.

[lopopolo]

Added some fixes to skip some known bad specs:

• Thread and Mutex block forever because they are single threaded.
• Module's access modifier story is sad which means we cannot load the fixtures.

Ruby spec now can run to completion for core!

$ RUST_BACKTRACE=1 cargo run --bin spec-runner ./**/*.rb
...
Passed 5412, skipped 998, not implemented 201, failed 8629 specs.

[lopopolo]

Filed upstream issue for Float#round spec slowness

https://github.com/mruby/mruby/issues/4566