feat: support fractional preload cache percentage

[akir-dev]

Description

Allow PreloadCache to use fractional percentage values with precision up to two decimal places.

Use case

For large movies over 50 GB, users storing the cache on disk may configure a large cache so the entire movie can fit in it. Currently, the minimum preload value is effectively 1%. With a large disk cache, even 1% can represent a
significant amount of data, resulting in unnecessarily long preloading before playback starts.

Fractional values such as 0.1% or 0.25% allow users to keep a large disk cache while configuring a much smaller preload buffer and starting playback sooner.

Changes

• Changed PreloadCache to support fractional values.
• Added rounding to two decimal places.
• Added a 0.01 step to the web interface.
• Updated Telegram settings and presets to parse and display fractional values.
• Updated the Swagger schema accordingly.