Fork reshape

Implements a fork-reshape pass in the scheduling language which can be used to coalesce a selection of fork-joins, interchange them into a specified order, and then split them into a specified series of chunks. Adds a parallel and tiled schedule for matmul that uses fork-reshape to keep the schedule quite clean.

Also adds tuples to the scheduling language and a new form of let-statements that allow destructing tuples, it's not the nicest (it's not a general pattern handler and will only cause an error if there are too many fields on the left-hand side, not too few, but it's enough to make the code that uses fork-reshape cleaner).

Includes a few other tweaks I ran into

• When adding a node in the editor, only insert an empty def_use set if the node doesn't have one yet (this is important due to cycles between nodes, and was causing issues in fork reshape since it invokes a series of passes using the same editor)
• Made fork-coalesce return the fork and join nodes when it succeeds so that they can be used in further operations.
• Modified fork coalesce's check for control flow between the forks and joins to check via uses rather than users because I was having weird issues with checking users
• Modified fork coalesce to perform everything as a single edit because I was having issues when manually scheduling matmul when using selections with coalesce.
• Modified fork split to return the ID of the new fork on a success
• Modified both fork split and coalesce to propagate parallel fork schedules when appropriate to avoid having to re-assign/re-infer schedules

hercules_opt/src/fork_transforms.rs

@@ -719,6 +719,11 @@ pub fn fork_coalesce_helper(
         };
         let new_fork = edit.add_node(new_fork);
 
+        if edit.get_schedule(outer_fork).contains(&Schedule::ParallelFork)
+            && edit.get_schedule(inner_fork).contains(&Schedule::ParallelFork) {
+            edit = edit.add_schedule(new_fork, Schedule::ParallelFork)?;
+        }
+
         edit = edit.replace_all_uses(inner_fork, new_fork)?;
         edit = edit.replace_all_uses(outer_fork, new_fork)?;
         edit = edit.replace_all_uses(outer_join, inner_join)?;
@@ -1271,6 +1276,9 @@ fn fork_interchange(
             edit = edit.delete_node(old_id)?;
         }
         let new_fork = edit.add_node(new_fork);
+        if edit.get_schedule(fork).contains(&Schedule::ParallelFork) {
+            edit = edit.add_schedule(new_fork, Schedule::ParallelFork)?;
+        }
         edit = edit.replace_all_uses(fork, new_fork)?;
         edit.delete_node(fork)
     });