Rename sleap_RTC to sleap_rtc for consistent lowercase naming

Changed directory name from sleap_RTC to sleap_rtc to follow Python
package naming conventions (lowercase with underscores). This ensures
consistency across the codebase and matches the package name defined
in pyproject.toml.

This rename was necessary because Git is case-sensitive while macOS
uses a case-insensitive filesystem by default, causing the directory
to appear as sleap_rtc locally but sleap_RTC on GitHub.

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Co-Authored-By: Claude <noreply@anthropic.com>

Author: alicup29