Change unix precision to seconds for timestamp property
The timestamp property in AMQP 0-9-1 is defined as a 64bit Unix timestamp, which is seconds since 1970/1/1 For reference -> https://github.com/rabbitmq/rabbitmq-message-timestamp/issues/16#issuecomment-314799434
This causes issues while reading in some of the client libraries which assume that the value is in seconds & parses this value incorrectly Example, java client library -> https://github.com/rabbitmq/rabbitmq-java-client/blob/23e7ba0e96d383c80f8da2fb23786a1111854f9a/src/main/java/com/rabbitmq/client/impl/ValueReader.java#L266
LGTM, but maybe needs to wait for a major version bump as it's clearly going to be a Breaking Change. Although I expect many people are not running into this.