Add Avro payload decoding with schema mapping

[raphael-solace]

Why: Gives schema-based event teams the same inspection quality for Avro that PrettyDump already provides for JSON, XML, SDT, and Protobuf.

Stack note: Builds on codex/decoder-spi.

Implementation notes:

• Default PrettyDump behavior remains unchanged unless the new flags are used.
• This branch is part of the 10-PR QoL series and should be reviewed in order.

Verification:

• JAVA_HOME="$HOME/AnypointCodeBuilder/java/jdk-17.0.13+11/Contents/Home" ./gradlew clean test installDist --no-daemon
• build/staged/bin/prettydump --help