Make HistoryService methods async

[progval]

We are going to need that for the PostgreSQL implementation

@spb This fails to compile with:

error[E0277]: Invalid command handler
  --> sable_ircd/src/command/handlers/chathistory.rs:47:1
   |
47 | #[command_handler("CHATHISTORY")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `for<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i> fn(&'a (dyn command::plumbing::Command + 'a), source_types::UserSource<'b>, &'c server::ClientServer, &'d (dyn command_response::CommandResponse + 'd), &'e str, &'f str, &'g str, &'h str, std::option::Option<&'i str>) -> impl futures::Future<Output = Result<(), command::error::CommandError>> {handle_chathistory}` is not a valid command handler
   |
   = help: the trait `handler::AsyncHandlerFn<'_, _, _>` is not implemented for fn item `for<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i> fn(&'a (dyn command::plumbing::Command + 'a), source_types::UserSource<'b>, &'c server::ClientServer, &'d (dyn command_response::CommandResponse + 'd), &'e str, &'f str, &'g str, &'h str, std::option::Option<&'i str>) -> impl futures::Future<Output = Result<(), command::error::CommandError>> {handle_chathistory}`
   = note: All parameter types must implement `AmbientArgument` or `PositionalArgument`
   = note: Return type must be `CommandResult`
note: required by a bound in `call_handler_async`
  --> sable_ircd/src/command/plumbing/mod.rs:55:29
   |
53 | pub(crate) fn call_handler_async<'ctx, 'handler, Amb, Pos>(
   |               ------------------ required by a bound in this function
54 |     ctx: &'ctx dyn Command,
55 |     handler: &'handler impl AsyncHandlerFn<'ctx, Amb, Pos>,
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `call_handler_async`
   = note: this error originates in the attribute macro `command_handler` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: Invalid command handler
  --> sable_ircd/src/command/handlers/chathistory.rs:47:1
   |
47 | #[command_handler("CHATHISTORY")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `for<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i> fn(&'a (dyn command::plumbing::Command + 'a), source_types::UserSource<'b>, &'c server::ClientServer, &'d (dyn command_response::CommandResponse + 'd), &'e str, &'f str, &'g str, &'h str, std::option::Option<&'i str>) -> impl futures::Future<Output = Result<(), command::error::CommandError>> {handle_chathistory}` is not a valid command handler
   |
   = help: the trait `handler::AsyncHandlerFn<'_, _, _>` is not implemented for fn item `for<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i> fn(&'a (dyn command::plumbing::Command + 'a), source_types::UserSource<'b>, &'c server::ClientServer, &'d (dyn command_response::CommandResponse + 'd), &'e str, &'f str, &'g str, &'h str, std::option::Option<&'i str>) -> impl futures::Future<Output = Result<(), command::error::CommandError>> {handle_chathistory}`
   = note: All parameter types must implement `AmbientArgument` or `PositionalArgument`
   = note: Return type must be `CommandResult`
note: required by a bound in `call_handler_async`
  --> sable_ircd/src/command/plumbing/mod.rs:55:29
   |
53 | pub(crate) fn call_handler_async<'ctx, 'handler, Amb, Pos>(
   |               ------------------ required by a bound in this function
54 |     ctx: &'ctx dyn Command,
55 |     handler: &'handler impl AsyncHandlerFn<'ctx, Amb, Pos>,
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `call_handler_async`

For more information about this error, try `rustc --explain E0277`.

any idea why?