Add download progress tracking and byte formatting utilities

- Introduced `fmt_bytes` function for human-readable byte size formatting.
- Added `DownloadProgress` class to track and display download progress with speed and completion percentage.
- Updated `download` functions in `civitai_fetch.py` and `llamacpp_fetch.py` to utilize progress tracking.
- Enhanced `ollama_pull.py` to support streaming progress updates during model pulls.
- Updated tests to validate new formatting and progress tracking functionalities, ensuring accurate output and user feedback.

tests/test_civitai_fetch.py

@@ -1,6 +1,6 @@
 from pathlib import Path
 
-from gpu_rent.remote.civitai_fetch import should_skip
+from gpu_rent.remote.civitai_fetch import fmt_bytes, progress_line, should_skip
 
 
 def test_should_skip_missing(tmp_path: Path):
@@ -33,3 +33,24 @@ def test_should_not_skip_bad_sha(tmp_path: Path):
     skip, reason = should_skip(dest, "deadbeef" * 8)
     assert skip is False
     assert "перекачиваю" in reason
+
+
+def test_fmt_bytes():
+    assert fmt_bytes(500) == "500B"
+    assert "KB" in fmt_bytes(2048)
+    assert "MB" in fmt_bytes(5 * 1024 * 1024)
+    assert "GB" in fmt_bytes(2 * 1024**3)
+
+
+def test_progress_line_with_total():
+    line = progress_line("file", 512 * 1024 * 1024, 1024 * 1024 * 1024, 10 * 1024 * 1024, width=10)
+    assert "[" in line and "]" in line
+    assert "50.0%" in line
+    assert "/s" in line
+    assert "file" in line
+
+
+def test_progress_line_unknown_total():
+    line = progress_line("file", 1024 * 1024, None, 100_000)
+    assert "%" not in line
+    assert "/s" in line