Fix aead negotation failure response

[davidv1992]

We used to return the same response for aead negotiation failures, as we did for next protocol negotiation failures. This makes those responses different.

As a side-effect, the error reporting for similar failures during monitoring is also improved.

Closes #408

[codecov]

Codecov Report

❌ Patch coverage is 95.34884% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.67%. Comparing base (bc3afde) to head (c8d3796).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
nts-pool-monitor/src/nts.rs	0.00%	4 Missing ⚠️
nts-pool-ke/src/pool_ke.rs	98.44%	2 Missing ⚠️
pool-nts/src/lib.rs	94.87%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #474      +/-   ##
==========================================
+ Coverage   70.32%   70.67%   +0.35%     
==========================================
  Files          68       68              
  Lines       14569    14732     +163     
==========================================
+ Hits        10245    10412     +167     
+ Misses       4324     4320       -4     

Flag	Coverage Δ
beta	70.90% <95.34%> (+0.34%)	⬆️
fuzz	60.48% <11.11%> (-1.13%)	⬇️
fuzz-client_request	35.39% <0.00%> (-1.13%)	⬇️
fuzz-key_exchange_response	40.66% <11.11%> (-1.11%)	⬇️
fuzz-record	35.28% <0.00%> (-0.66%)	⬇️
fuzz-server_information_response	24.51% <0.00%> (-0.93%)	⬇️
msrv	70.57% <95.34%> (+0.34%)	⬆️
stable	70.88% <95.34%> (+0.31%)	⬆️
test	70.60% <95.34%> (+0.35%)	⬆️
x86_64-unknown-linux-gnu	70.60% <95.34%> (+0.35%)	⬆️
x86_64-unknown-linux-musl	70.87% <95.34%> (+0.30%)	⬆️

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[squell]

Would there be a benefit in using Result<Result<(ProtocolId, AlgorithmDecription), NegotiationError>, PoolError>?

[squell]

This fixes the issue:

$ ./demo localhost 256_GCM_SIV
GnuTLS: (TLS1.3)-(ECDHE-SECP256R1)-(RSA-PSS-RSAE-SHA512)-(AES-256-GCM)
NTS error: NO_AEAD (read: 14 bytes)