feat: implement `Default` for `RwSignal` and `StoredValue` (#1877) #1008

Job	Run time
get-leptos-changed / Detect Source Change	5s
CI (integrations/actix) / Run ci (nightly)	23m 6s
CI (integrations/axum) / Run ci (nightly)	20m 21s
CI (integrations/utils) / Run ci (nightly)	15m 56s
CI (integrations/viz) / Run ci (nightly)	16m 44s
CI (leptos) / Run ci (nightly)	1h 48m 45s
CI (leptos_config) / Run ci (nightly)	15m 11s
CI (leptos_dom) / Run ci (nightly)	26m 28s
CI (leptos_hot_reload) / Run ci (nightly)	14m 38s
CI (leptos_reactive) / Run ci (nightly)	46m 48s
CI (leptos_server) / Run ci (nightly)	36m 37s
CI (meta) / Run ci (nightly)	16m 49s
CI (leptos_macro) / Run ci (nightly)	33m 35s
CI (server_fn) / Run ci (nightly)	17m 17s
CI (router) / Run ci (nightly)	24m 56s
CI (server_fn_macro) / Run ci (nightly)	18m 32s
CI (server_fn/server_fn_macro_default) / Run ci (nightly)	14m 23s
	7h 30m 11s

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