Erase transient progress lines and coordinate shared grace period across embedders

[sigurdm]

• Erase transient progress lines using ANSI escape sequences (\r\u001b[2K, log.eraseLine) on supported terminals in Progress.stopAndClear (with whitespace overwrite fallback for non-ANSI terminals).
• Support transient progress via log.progress(..., transient: true) and use it during dependency resolution (summaryOnly: true), cached package downloads, and snapshot precompilation so progress output is erased upon completion.
• Add ProgressGracePeriod to debounce transient progress display (defaulting to 500ms), sharing the grace period across multiple operations and across Zone boundaries (accessible to embedding tools via withOverrides(progressGracePeriod: ...)).
• Reset the active grace period whenever permanent log output is printed.
• Suppress the summary message in SolveReport when quiet: true (e.g. during embedded dart run).
• Add unit tests in test/progress_test.dart.

Companion Dart SDK CL: https://dart-review.googlesource.com/c/sdk/+/538280

cc @mit-mit

[sigurdm]

Here are side-by-side recordings comparing the baseline behavior with this PR.
These were recorded with a simulated network delay (~350ms per request) to clearly showcase the spinner animation, elapsed time ticker, and subsequent cleanup.

In every recording:

• Left (Red badge): Dart 3.13 baseline behavior
• Right (Green badge): Clean transient progress (this PR)

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1. Cold Start: dart run bin/hello.dart

Resolving and downloading package dependencies prior to running an application. In baseline, intermediate resolution and download progress lines remain permanently above the app output. In the updated version, transient spinners animate during network operations and are erased before the app executes.

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2. Standalone Compilation: dart compile exe bin/hello.dart -o hello.exe

Compiling a Dart entrypoint to a self-contained native executable. The resolution and download spinners spin and tick during dependency acquisition, and are then erased before the compiler output is rendered.

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3. Dependency Graph: dart pub deps

Inspecting the project's dependency graph. In baseline, Resolving dependencies... and Downloading packages... clutter the terminal before the tree. In the updated version, transient progress erases in place, leaving only the clean dependency tree.

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4. Sub-project Example: dart pub get --example

Resolving dependencies for both a package and its nested ./example sub-project. In baseline, both sets of progress indicators stay in the output. In the updated version, intermediate progress for ./example is transient and erases cleanly to Got dependencies in ./example..

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5. Remote Package Run: dart run <remote-package>

Executing an executable from an uncached remote package (e.g. dart run benchmark_harness:bench@ --help). In baseline, Resolving dependencies in ..., Downloading packages..., and compiler output (Generated: ...) remain permanently above the command output. In the updated version, resolution and download spinners are transient and erased upon completion, and non-error compiler output is silenced.