feat: allow overlapping hooks

[jaypaik]

Motivation

The spec is not explicit about how the account should treat overlapping hooks (identical hooks that are applied on the same execution function selector by one or more plugins). Although reuse of hook functions across plugins may be uncommon, allowing overlaps helps in the case where multiple plugins opt to use the short-circuit magic value FunctionReference._PRE_HOOK_ALWAYS_DENY as a way to protect a particular function.

This is also a step toward potentially allowing multiple validation functions to be applied to a given selector.

Solution

Use an EnumerableMap to keep track of the number of overlaps, to be able to keep the account in a consistent state when overlapping hooks are uninstalled.

When running the hooks, the following strategy is applied.

1. Coalesce all exact duplicate pairs of hooks, and execute them only once.
2. If there are two hook pairs that have the same pre-exec hook but have different post-exec hooks, the pre-exec should be executed twice - once for each of the corresponding post-exec hook - and the return data from each should be passed to them. Same applies for two pairs of hooks that have the same post-exec hook but different pre-exec hooks.

Additional changes

• I've bumped up the forge-std version to be able to use vm.expectCall with the count parameter.
• Added isEmpty() to FunctionReferenceLib and updated code to use it over direct comparisons.
• Order of associated post hook executions have been reversed to follow the middleware pattern of executing pre/post processing steps in layers.

[adam-alchemy]

Looks good!