Fix long filename handling for byte-based filesystem limits

[LiuqingDu]

Description

This PR fixes OSError: [Errno 36] File name too long when generated output filenames exceed the filesystem byte limit.

The issue is more likely with CJK titles because filename limits are byte-based, not character-based. For example:

2-01 Medley_ 前程锦绣 _ 喜气洋洋 _ 甜蜜如软糖 _ 流非飞 _ 不羁的风 (Live).m4a

The ASCII characters are mostly 1 byte each, while each Chinese character is usually 3 bytes in UTF-8. So a filename can be under 255 visible characters but still exceed the common 255-byte filename limit.

This is not limited to Chinese. Any filename containing many non-ASCII characters can hit this issue, including Japanese, Korean, emoji, and other writing systems. The filename may look shorter than 255 visible characters, but still exceed the filesystem's byte-based limit because UTF-8 encodes many of these characters as multiple bytes.

Changes

gamdl/downloader/base.py

• Caps each generated path component at 255 UTF-8 bytes.
• Applies --truncate as a smaller byte limit when provided.
• Counts the file extension inside the filename byte budget.

gamdl/cli/cli.py

• Stops writing download entries to the database after unexpected download errors.

gamdl/cli/database.py

• Treats unstatable historical database paths as missing, so old bad entries do not crash future runs.