Use generics to generalize int32/int64/float32/float64 to number encoder/decoder/store

[akrennmair]

This PR introduces Go 1.18 generics to generalize the separate int32/int64/float32/float64 implementation into a single number type with small specializations. This deduplicates a lot of similar code across these types.

Since this required a switch to Go 1.18, I also replaced interface{} with the new any type. I also migrated the existing fuzz tests for gofuzz with Go 1.18 fuzz tests.

And finally, I removed the vendor subdirectory as it caused issues and doesn't really make sense for a library.

[akrennmair]

Looks like golangci-lint isn't quite mature enough to lint this code. Converting to draft for now...

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 92.47059% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.27%. Comparing base (e6b70a8) to head (d41620e).
⚠️ Report is 26 commits behind head on master.

Files with missing lines	Patch %	Lines
cmd/parquet-tool/cmds/readfile.go	0.00%	5 Missing ⚠️
deltabp_decoder.go	76.19%	2 Missing and 3 partials ⚠️
type_number.go	92.59%	3 Missing and 1 partial ⚠️
deltabp_encoder.go	78.57%	2 Missing and 1 partial ⚠️
helpers.go	75.00%	1 Missing and 2 partials ⚠️
chunk_writer.go	90.00%	2 Missing ⚠️
floor/interfaces/marshaller.go	85.71%	2 Missing ⚠️
floor/interfaces/unmarshaller.go	75.00%	2 Missing ⚠️
schema.go	85.71%	1 Missing and 1 partial ⚠️
type_dict.go	77.77%	2 Missing ⚠️
... and 2 more
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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #83      +/-   ##
==========================================
+ Coverage   86.73%   87.27%   +0.53%     
==========================================
  Files          48       46       -2     
  Lines        9777     9444     -333     
==========================================
- Hits         8480     8242     -238     
+ Misses        939      884      -55     
+ Partials      358      318      -40     

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