Fix acceptor Logon reset flag when ResetOnLogon is enabled

[6democratickim9]

Fixes #762.

When an acceptor resets its sequence numbers because ResetOnLogon=Y,
include ResetSeqNumFlag(141)=Y in its Logon response for FIX 4.1
and later. Preserve the existing handling of an incoming reset flag.

Add a regression test for a Logon without an incoming reset flag,
and update acceptance-test expectations for affected sessions.

Validation:

• Regression test fails before the fix and passes afterward.
• Root package tests with the race detector passed.
• go vet, build, and the full unit suite with MongoDB passed.
• golangci-lint v1.64.6 passed using Go 1.24.0.
• All acceptance matrix cases in the local validation script passed,
  including both decimal implementations.