Fix: Add some simple limits to Electrum RPC by default

[junderw]

I wonder if the defaults should be set low or maybe a little higher.

Either way I have set fairly high limits for the start script.

[Copilot]

Pull request overview

This PR introduces default resource limits for the Electrum RPC server (request line size, per-connection subscription count, and concurrent client connections) and wires them through configuration/launch scripts to reduce abuse and accidental overload.

Changes:

• Add new CLI/config options: --electrum-max-line-size, --electrum-max-subscriptions, --electrum-max-clients.
• Enforce per-connection subscription limits and a global max-client limit in the Electrum server.
• Update the start script to pass the new limits (with higher overrides for specific hosts/networks).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
start	Passes new Electrum limit flags with defaults and host-based overrides.
src/electrum/server.rs	Implements max request line size enforcement, per-client subscription cap, and max concurrent client connections.
src/config.rs	Adds config fields and clap args/defaults for the new Electrum limits.

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