Use specialization feature for AnyTryInto trait

[cowboy-bebug]

Refactor src/interpreter/type_cast.rs to

• use specialization
• have default impl (with default return)
• refactor Any -> TryInto

[cowboy-bebug]

What we expected from specialization was something like:

// Parent (default) impl
impl<'a, T, U> PactTryInto<'a, T> for U { ... }
// Child (specialised) impl
impl<T: TryInto<u64>> PactTryInto<'a, T> for PactType<'a> { ... }
impl<T: AsRef<[u8]>>  PactTryInto<'a, T> for PactType<'a> { ... }

But the above impl blocks are non-overlapping to raise conflicting trait implementations error as the compiler doesn't know which of the children impl blocks to choose.

To make the above compile, the following can be observed:

// Parent (default) impl
impl<T: TryInto<u64>> PactTryInto<'a, T> for PactType<'a> { ... }
// Child (specialised) impl
impl<T: TryInto<u64> + AsRef<[u8]>>  PactTryInto<'a, T> for PactType<'a> { ... }

However, this is not what we want.

The issue could be revisited once specialization overlap rules are enhanced (see rust-lang/rust#42721 (comment) and rust-lang/rust#49624)