feat: oxidize streaming_brief feature

[bepri]

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I recommend reviewing per-commit.

Adds back the streaming_brief feature, which really only is noticeable in a niche circumstance where streaming_brief=True and a logging event with a verbosity level > logging.DEBUG is received. Below is a minimal script to demonstrate this behavior.

import logging
import subprocess
from time import sleep

from craft_cli import EmitterMode
from craft_cli._rs.emitter import Emitter

logger = logging.getLogger(__name__)

e = Emitter("blah.log", EmitterMode.BRIEF, "example.com", "Hello", streaming_brief=True)
logger.info("Testing")
with e.open_stream("Counting") as pipe:
    for i in range(5):
        logger.info("Printing %d", i)
        sleep(0.3)
        subprocess.run(["echo", str(i)], check=True, stdout=pipe)
        sleep(0.3)

e.message("Done")

As a fly-by, this adds back the ability to prefix messages piped with Emitter.open_stream, as mentioned at #416 (comment). This behavior is shown in the testing script as well.

[mr-cal]

LGTM

[Copilot]

Pull request overview

This PR reintroduces the streaming_brief behavior in the Rust-backed emitter/logging path, and adds infrastructure to prefix terminal output (notably for open_stream) while simplifying the printer’s message model.

Changes:

• Add streaming_brief plumbing into Emitter and LogListener to allow streaming library logs in brief mode.
• Refactor printer message handling to rely on a new Message.permanent flag (and simplify MessageType usage).
• Add a global, printer-managed prefix that can be applied to emitted messages.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/emitter.rs	Adds streaming_brief, updates verbosity comparisons, and introduces open_stream(prefix=...) plus prefix helpers.
src/logs.rs	Adds streaming_brief handling for brief-mode logging decisions and sets Message.permanent for log records.
src/printer.rs	Introduces Message.permanent, adds prefix support, and simplifies routing to be target-based.
src/streams.rs	Updates stream-to-printer messages to use permanent + MessageType::Text.

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[tigarmo]

LGTM thanks. I'll point out that what you called a 'niche' circumstance is really the main way that users get feedback from our apps todays (streaming brief is the default, and the build messages are shown as 'info' logs)

[bepri]

I'm only calling it niche in the sense that the exact set of requirements "must be in brief mode, with streaming_brief, and only via logging records of the right verbosity level" makes it a surprisingly narrow path a message must follow to see this behavior. When I was reviewing the original code, I doubted my own interpretation because it seemed like there should've been more to it than that, heh

[bepri]

Force-pushed to clean up commit history.