Change inherent methods returning owned types into `(Try)From` impls

[codecov[bot]]

Codecov Report

Base: 78.34% // Head: 78.28% // Decreases project coverage by -0.06% :warning:

Coverage data is based on head (dfd61f7) compared to base (9785331). Patch coverage: 94.87% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## prīmum #96 +/- ## ========================================== - Coverage 78.34% 78.28% -0.07% ========================================== Files 6 6 Lines 351 350 -1 ========================================== - Hits 275 274 -1 Misses 76 76 ``` | [Impacted Files](https://codecov.io/gh/Nullus157/bs58-rs/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157) | Coverage Δ | | |---|---|---| | [src/alphabet.rs](https://codecov.io/gh/Nullus157/bs58-rs/pull/96/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157#diff-c3JjL2FscGhhYmV0LnJz) | `70.37% <ø> (ø)` | | | [src/lib.rs](https://codecov.io/gh/Nullus157/bs58-rs/pull/96/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157#diff-c3JjL2xpYi5ycw==) | `100.00% <ø> (ø)` | | | [src/encode.rs](https://codecov.io/gh/Nullus157/bs58-rs/pull/96/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157#diff-c3JjL2VuY29kZS5ycw==) | `78.43% <77.77%> (ø)` | | | [src/decode.rs](https://codecov.io/gh/Nullus157/bs58-rs/pull/96/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157#diff-c3JjL2RlY29kZS5ycw==) | `58.55% <100.00%> (ø)` | | | [tests/decode.rs](https://codecov.io/gh/Nullus157/bs58-rs/pull/96/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157#diff-dGVzdHMvZGVjb2RlLnJz) | `100.00% <100.00%> (ø)` | | | [tests/encode.rs](https://codecov.io/gh/Nullus157/bs58-rs/pull/96/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157#diff-dGVzdHMvZW5jb2RlLnJz) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Nullus157)

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