Progress Feedback for build command

[Mateus-Cordeiro]

This PR adds structured progress feedback to the build command, usable both from the CLI and from SDK callers.

Changes

Progress API

• Introduces a lightweight ProgressCallback and a small set of ProgressEvent kinds to report:
  • build start/finish
  • datasource start/finish
  • datasource progress
• Uses a ProgressEmitter

Build pipeline wiring

• Threads ProgressCallback (optional) through the build entrypoints.
• Emits lifecycle events during execution

CLI progress rendering (Rich)

• Adds a rich_progress() context manager that renders:
  • an overall Datasources i/n progress bar
  • a per datasource progress bar
  • per datasource completion lines + final summary message
• Disabled when not running in an interactive terminal
• Set as an optional cli extra with fallback to no-op if rich isn't installed.

Screen.Recording.2026-02-10.at.11.06.41.mov