fix: guard .strip() on multimodal content and log prepare_call exceptions

Fixes #4800 and #4805.

Changes

• #4800: Guard msg.content.strip() calls with isinstance() check in loop.py — prevents crash when multimodal content returns non-string content
• #4805: Replace suppress(Exception) with explicit try/except + logger.exception() in runner.py — ensures prepare_call failures are logged instead of silently swallowed

(The aiohttp dependency fix for #4829 was removed from this PR — already addressed in #4830 by @alekwo.)

Verification

• Tests: 1243 pass | Lint: clean | Diff: 2 files, +7/-4

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Co-Authored-By: Claude noreply@anthropic.com Co-Authored-By: Happy yesreply@happy.engineering