Rework erldns_handler to be performant and type-safe

[NelsonVides]

Uses persistent_term instead of ETS tables, and callbacks are preallocated instead of resolved at runtime again and again. Same optimisations than zone codecs or pipelines had.

This will be useful when reworking specially the resolver, as currently so much code internal to the handlers is scattered there and in the dnssec module. It also clearly defines a behaviour for this module, as callbacks were not specified.

[coveralls]

Pull Request Test Coverage Report for Build 16138661929

Details

• 45 of 61 (73.77%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+1.3%) to 82.121%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/erldns_handler.erl	38	54	70.37%

Files with Coverage Reduction	New Missed Lines	%
src/erldns_handler.erl	1	69.49%

Totals
Change from base Build 16137778602:	1.3%
Covered Lines:	1208
Relevant Lines:	1471

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💛 - Coveralls