feat: do not use open servers unless explicitly specified

[Yan-Muzi]

No description provided.

[Copilot]

Pull request overview

This PR modifies the server selection logic to exclude "open" servers by default, filtering to only use servers that start with "node" unless explicitly specified via the server_list parameter. This change is motivated by performance concerns, as noted in the comment that open servers are too slow.

Changes:

• Modified server selection logic to filter out "open" servers by default when server_list is "all" or empty
• Added explanatory comment about why open servers are excluded
• Applied filtering using lambda function to check server names starting with "node"

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[Copilot]

Typo in variable name: 'serer_pool' should be 'server_pool'. The word 'server' is misspelled as 'serer'. Although the code is internally consistent (using 'serer_pool' on lines 162-164), this typo makes the code harder to read and maintain.

Suggested change

	serer_pool = list(filter(lambda s: s.startswith("node"), SERVER_POOL))
	desired_sever_num = min(len(self.checkpoints) // 64 + 1, len(serer_pool))
	server_pool = random.sample(serer_pool, k=desired_sever_num)
	server_pool = list(filter(lambda s: s.startswith("node"), SERVER_POOL))
	desired_sever_num = min(len(self.checkpoints) // 64 + 1, len(server_pool))
	server_pool = random.sample(server_pool, k=desired_sever_num)