Clarify how to share `TokenBucket` and `ClientRateLimiter`

/// Represents the retry partition, e.g. an endpoint, a region

///

/// By default, a retry partition created via [`RetryPartition::new`] uses built-in token bucket and rate limiter settings,

/// with no option for customization.

/// A retry partition created with [`RetryPartition::new`] uses built-in

/// token bucket and rate limiter settings, with no option for customization.

/// Default partitions with the same name share the same token bucket

/// and client rate limiter.

///

/// To configure these components, use a custom retry partition created via [`RetryPartition::custom`].

/// Custom partitions allow full control over token bucket and rate limiter.

/// To customize these components, use a custom retry partition via [`RetryPartition::custom`].

/// A custom partition owns its token bucket and rate limiter, which:

/// - Are independent from those in any default partition.

/// - Are not shared with other custom partitions, even if they have the same name.

///

/// Two `RetryPartition`s that are equal, as defined by the `Eq` trait, share the same token bucket and client rate limiter.

/// This means that the token bucket and rate limiter in a custom retry partition are independent

/// of those in a default retry partition, even if the custom partition has the same name as the default partition.

/// To share a token bucket and rate limiter among custom partitions,

/// either clone the custom partition itself or clone these components

/// beforehand and pass them to each custom partition.

#[non_exhaustive]

#[derive(Clone, Debug)]

pub struct RetryPartition {