eth/abi: enable packed encoding

[q9f]

fix #103

• [x] uint
• [x] int
• [x] bool
• [x] string / bytes
• [ ] ufixed
• [ ] fixed
• [ ] tuple
• [x] hash
• [x] address

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 98.90110% with 1 line in your changes missing coverage. Please review.

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:exclamation: Current head 6b712bb differs from pull request most recent head 1d4c456

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Files	Patch %	Lines
lib/eth/abi/encoder.rb	96.77%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #211 +/- ## ======================================= Coverage ? 99.75% ======================================= Files ? 77 Lines ? 4412 Branches ? 0 ======================================= Hits ? 4401 Misses ? 11 Partials ? 0 ```

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