[wenjin272]

Linked issue: N/A

Purpose of change

The release-0.3 branch was created for the 0.3 release, but the release
process step that updates main to the next development version was missed.

This change updates the project development version to 0.4:

• Maven modules use 0.4-SNAPSHOT.
• The Python package uses 0.4.dev0.
• Documentation metadata and python/jar_manifest.json use 0.4-SNAPSHOT.
• Cross-language tests reference the new 0.4-SNAPSHOT test JAR name.

The released version defaults in tools/install.sh remain unchanged.

Tests

• ./tools/build.sh --java (all 34 Maven modules built successfully; tests are
  skipped by the build script)
• git diff --check
• Verified that no 0.3-SNAPSHOT or 0.3.dev0 development-version references
  remain

API

No public API changes.

Documentation

• doc-needed
• doc-not-needed
• doc-included

Was this patch authored or co-authored using generative AI tooling?

• Yes
• No