Implement ChaCha20-Poly1305 Crypto Primitive

[adrianosela]

Implement ChaCha20-Poly1305 Crypto Primitive

Adds encrypt/decrypt with ChaCha20-Poly1305.

ChaCha20-Poly1305, CCM, and GCM are all AEAD based, so I've refactored the encrypt/decrypt logic into a generic aead implementation.

Also refactors all the common code in all the benchmark tests into helper functions benchmarkEncrypt and benchmarkDecrypt

The refactor also includes using buffer-pools for nonces for all of the ciphers... which comes with some nice side effects. Performance is neutral to slightly better for the refactored cipher implementations (CCM and GCM), and memory allocations per operation are reduced:

CCM:

• Encrypt: 7 allocs (same as original)
• Decrypt: 9 → 7 allocs (-2 allocations, -16 to -24 bytes)

GCM:

• Encrypt: 4 → 3 allocs (-1 allocation, -16 bytes)
• Decrypt: 3 → 2 allocs (-1 allocation, -16 bytes)

Note that the new ChaCha20-Poly1305 crypto primitive is currently unused. Next PR will add full cipher suite implementations (TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256, etc...) which will make use of this code.

[codecov]

Codecov Report

❌ Patch coverage is 89.10891% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.88%. Comparing base (9495bef) to head (8ed00b7).

Files with missing lines	Patch %	Lines
pkg/crypto/ciphersuite/ciphersuite.go	88.33%	6 Missing and 1 partial ⚠️
pkg/crypto/ciphersuite/chacha20poly1305.go	80.95%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #789      +/-   ##
==========================================
+ Coverage   81.72%   81.88%   +0.16%     
==========================================
  Files         108      109       +1     
  Lines        6062     6072      +10     
==========================================
+ Hits         4954     4972      +18     
+ Misses        712      706       -6     
+ Partials      396      394       -2     

Flag	Coverage Δ
go	81.88% <89.10%> (+0.16%)	⬆️

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