Co-authored-by: qcorradi <q.corradi22@imperial.ac.uk>
Co-authored-by: Zachary Snow <zach@zachjs.com>

- event expressions use Expr over LHS
- stricter AST representation of event controls
- property specs use event expressions directly

- updated representation and added codegen for sequence match items
- fix incorrect codegen for `iff` property expression

- moved 4 phases to initial set and 3 to final set
- fix synthetic unnamed genblocks preventing name resolution
- asgnop conversion folds in unisub when possible

- convert loops with no or many incrementations
- restrict AST node to only contain traditional initializations
- parser elaborates for loop decls into a synthetic block
- decl list codegen is now specific to parameter decl lists
- update jump conversion special cases for new representation
- first experiments with bimapM

Disabling the package item injection routine used in the enum conversion
when there were no items to inject exposed cases where conversions would
generate duplicate declarations. The hierarchical constant and param
type conversions were trivially affected. The package conversion could
inject class items within a generate region and then re-inject them
outside of that generate region. The package conversions now uses an
upgraded generate region flattening utility to ensure injected class
items are seen. This also includes coverage for a conflict which
occurred even without the enum conversion change.

- fix int type conversion not visiting function return type expressions
- add node-based traversal for decls visiting top level types and exprs
- explicit expr and type recursion in package ident resolution
- expose mapBothM traversal helper
- avoid double-visiting of decl types in certain conversions

- support for additional assignment statements in loop initializations
- greatly improved error messaging in these contexts
- decl parser takes in the ending token; significant related refactoring
- pass through elaboration system tasks
- removed non-blocking assignment operator precedence hack
- preliminary nosim test suite for features unsupported by iverilog

- new net decl to replace net pseudo-type
- support nets with complex base types, including typenames
- support var declaration type prefix for all data types
- support var as lone type shorthand
- refactor AST representation of strengths
- traversal helpers for treating nets as variables
- use decl traversals where appropriate

- pattern keys now represented as TypeOrExpr
- support for simple integer struct pattern keys

- avoid premature conversion of default struct type parameters
- allow use of $clog2, $signed, and $unsigned in type parameters
- more thorough and efficient top reference ident renaming
- precede type param conversion with hier const pass

- delegate cast type and sign resolution to TypeOf conversion
- internal support for injecting data declarations into statements
- fix size and sign of unbased unsized literals used in casts
- avoid generating many unnecessary explicit casts
- support casts which depend on localparams within procedures
- expression traversal correctly visits types within type casts
- fix typeof on expressions of net types
- handle additional edge cases for unsized integer array patterns
- preserve signedness of implicitly flattened unpacked integer arrays

- full import and export support
- simplify AST representation of import and export
- allow package-scoped identifiers invoked as subroutines
- use scoped name resolution for identifiers in packages
- merge package item nesting conversion into package conversion
- fix handling of colliding enum items in separate modules
- fix visiting enum item exprs in types