feat: standardize on a `Callback` type that is `Copy` (#1795) #893

Job	Run time
get-leptos-changed / Detect Source Change	9s
CI (integrations/actix) / Run ci (nightly)	20m 39s
CI (integrations/axum) / Run ci (nightly)	17m 21s
CI (integrations/utils) / Run ci (nightly)	17m 32s
CI (integrations/viz) / Run ci (nightly)	15m 27s
CI (leptos) / Run ci (nightly)	1h 27m 42s
CI (leptos_config) / Run ci (nightly)	18m 2s
CI (leptos_dom) / Run ci (nightly)	27m 34s
CI (leptos_hot_reload) / Run ci (nightly)	15m 39s
CI (leptos_macro) / Run ci (nightly)	25m 2s
CI (leptos_reactive) / Run ci (nightly)	42m 43s
CI (leptos_server) / Run ci (nightly)	34m 18s
CI (meta) / Run ci (nightly)	16m 35s
CI (router) / Run ci (nightly)	17m 14s
CI (server_fn) / Run ci (nightly)	19m 11s
CI (server_fn_macro) / Run ci (nightly)	17m 32s
CI (server_fn/server_fn_macro_default) / Run ci (nightly)	14m 56s
	6h 47m 36s

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