Print a warning if a legacy JSON-RPC function is used

[tomaka]

cc #2804

Most legacy JSON-RPC functions can't be implemented properly by smoldot.

The situation kind of sucks, as the new JSON-RPC functions aren't stable and aren't implemented in Substrate yet.

However, the fact that the replacement isn't ready yet doesn't remove the fact that the old ones don't work properly. Therefore I think it's appropriate to print this warning.

The main reason why I'd like to print this warning is to raise awareness to anyone reading the logs of the fact that things might not work properly, and that it's not necessarily smoldot's fault but usually the API's fault.

[mergify]

Automatically approving tomaka's pull requests. This auto-approval will be removed once more maintainers are active.

[github-actions]

twiggy diff report

Difference in .wasm size before and after this pull request.

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 Delta Bytes │ Item
─────────────┼──────────────────────────────────────────────────────────────────────────────────────────────────────
      +11258 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h4e5535d74f64a010
      -10919 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hd2e16a9f83ad73f8
       +6016 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h2cfcd4756022494a
       -6016 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hfce84ea771fa5a69
       +5947 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h25301baaa6187ac0
       -5947 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::haa28720903ee7c9b
       -4535 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h19fe401542381413
       +4535 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h549529d6c485484d
       -3219 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h19d51823682a82b1
       +3219 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hccc18bf28263ab13
       -2888 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h43ed80633c783b1e
       +2888 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hd0c91d815c239c7b
       -2615 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h7bbfcc91e8a9c696
       +2615 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hfba2ebb862d1f219
       +2061 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h37cd9fb9d37b1b6e
       -2061 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h640bf07cf9c6be20
       -2045 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h06903141f29aef22
       +2045 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hc30da7609fdd4925
       -1959 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h3cd1d03d32b932d4
       +1959 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hba67734a1ba502b0
       +1110 ┊ ... and 443 more.
       +1518 ┊ Σ [463 Total Rows]