Simplify.Mail 2.2

Added

• BCC recipient support on all multi-recipient overloads
• IAntiSpamPool / AntiSpamPool extracted from MailSender with O(m) queue-based expiry and configurable max-items eviction (default 10 000) to prevent OOM
• MailSender.DefaultAntiSpamPool static property to swap the pool implementation without constructor injection
• Port validation in MailSenderSettings (throws ArgumentOutOfRangeException on out-of-range values)

Fixed

• Double-checked locking in SmtpClient getter replaced with Lazy<SmtpClient>(ExecutionAndPublication) for correct thread-safety on all architectures
• Dispose no longer disposes SemaphoreSlim while another thread may hold it; blocks until in-flight send completes, then disposes cleanly
• CheckAntiSpamPool redundant ContainsKey check removed
• Integration test assertions added for construction and port default

Performance

• SendSeparately / SendSeparatelyAsync now holds the SMTP lock for the entire batch instead of per-recipient acquire/release
• Anti-spam pool expiry uses queue-based O(m) scan instead of full O(n) dictionary enumeration