Modernize Wasmi differential fuzzing

[Robbepop]

Closes #896.

• New differential fuzzer now always fuzzes one arbitrarily chosen oracle (Wasmi (stack) or Wasmtime for now) in each iteration.
• Non-deterministic errors are now properly handled.
• All non-trivial implementation details reside in the new wasmi_fuzz crate which is better for maintenance.
  • This makes it much simpler to add new differential fuzzing oracles, e.g. Wasmer.
• Global state (globals and memory) are now properly checked for runs which are deterministic.
• Function call parameters are now arbitrarily chosen.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 367 lines in your changes missing coverage. Please review.

Project coverage is 80.30%. Comparing base (c33ccf7) to head (c6bea90).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/fuzz/src/oracle/wasmi.rs	0.00%	104 Missing ⚠️
crates/fuzz/src/oracle/wasmi_stack.rs	0.00%	101 Missing ⚠️
crates/fuzz/src/oracle/wasmtime.rs	0.00%	92 Missing ⚠️
crates/fuzz/src/oracle/exports.rs	0.00%	32 Missing ⚠️
crates/fuzz/src/value.rs	0.00%	21 Missing ⚠️
crates/fuzz/src/oracle/mod.rs	0.00%	15 Missing ⚠️
crates/fuzz/src/error.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1257      +/-   ##
==========================================
- Coverage   81.40%   80.30%   -1.11%     
==========================================
  Files         307      312       +5     
  Lines       25211    25559     +348     
==========================================
+ Hits        20523    20524       +1     
- Misses       4688     5035     +347     

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