Add ffmpeg progress updates during file handling

[gistrec]

Summary

• add ffmpeg scheduler to periodically update the preparation message with download and conversion progress
• track download and conversion progress in the file handler and ensure updates are reflected in Telegram
• allow safe message editing with multiple text fragments and register the new scheduler

Testing

• python -m compileall handlers schedulers utils

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Codex Task

[sentry]

Bug: Error message string in handlers/file.py is not an f-string, causing {duration_str} to display literally.
_{Severity: CRITICAL | Confidence: High}

🔍 Detailed Analysis

The string literal for the error message "Файл слишком длинный: {duration_str}\n" in handlers/file.py:115-117 is not an f-string. As a result, the {duration_str} placeholder is not interpolated, and users will see the literal text {duration_str} instead of the actual formatted duration. This makes the error message confusing and unhelpful, breaking the intended user experience.

💡 Suggested Fix

Change the string literal to an f-string: f"Файл слишком длинный: {duration_str}\n" in handlers/file.py:115.

🤖 Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: handlers/file.py#L115

Potential issue: The string literal for the error message "Файл слишком длинный:
{duration_str}\n" in `handlers/file.py:115-117` is not an f-string. As a result, the
`{duration_str}` placeholder is not interpolated, and users will see the literal text
`{duration_str}` instead of the actual formatted duration. This makes the error message
confusing and unhelpful, breaking the intended user experience.

_{Did we get this right? 👍 / 👎 to inform future reviews.
Reference ID: 4382644}