refactor(logging): simplified prints and add spinner

[yxlao]

TLDR

Displays spinner while streaming:

┌ request model=deepseek-v4-pro effort=max messages=167
├ context status=ok reasoning=57
└ ⠹

When done:

┌ request model=deepseek-v4-pro effort=max messages=167
├ context status=ok reasoning=57
└ stats   prompt=46,091 output=283 reasoning=59 cache_hit=99.4%

Summary

Extract logging utilities into a dedicated module, add a terminal spinner for streaming requests, and simplify both startup and per-request log output.

Changes Made

• New file src/deepseek_cursor_proxy/logging.py:
  • ConsoleLogFormatter — custom formatter that hides timestamps/level prefixes in normal mode and shows full detail in verbose mode
  • configure_logging() — sets up a StreamHandler with the appropriate formatter
  • TerminalSpinner — animated spinner (Braille frames) for tty streams during streaming requests
• server.py:
  • Replaced inline logging usage with from .logging import LOG, TerminalSpinner, configure_logging
  • Added TerminalSpinner lifecycle around streaming upstream requests (start before forwarding, stop on completion/error/disconnect)
  • Simplified startup logging: collapsed multiple LOG.info calls into concise key-value pairs, conditional on verbose mode
  • Removed tool_count from request log line; renamed ┌ cursor to ┌ request; simplified log_context_summary status output
  • Moved log_send_summary behind verbose gating
• transform.py and tunnel.py:
  • Replaced import logging + LOG = logging.getLogger(...) with from .logging import LOG
• tests/test_server.py:
  • Added unit tests for ConsoleLogFormatter (info/warning formatting, verbose timestamp) and TerminalSpinner (tty vs non-tty behavior)
  • Updated integration test assertions to match new log message format