This commit addresses #4041 by making the transaction::Version field private
Changes:
- Make the `Version` field private with `pub(crate)`
- Rename `non_standard` to `maybe_non_standard` for clarity since it accepts both standard and non-standard versions
- Add `#[inline]` attributes to small, frequently used methods:
- `as_u32`
- `maybe_non_standard`
Users now must use either:
- Constants (`Version::ONE/TWO/THREE`) for standard versions
- `maybe_non_standard` method for any version (standard or non-standard)
cb270eae8e