timed-map 1.6.0

Lightweight map implementation that supports expiring entries and fully compatible with both std and no_std environments.
Documentation 
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# timed-map

Lightweight map implementation that supports expiring entries and fully
compatible with both `std` and `no_std` environments.

`TimedMap` allows storing key-value pairs with optional expiration times. Expiration is
handled by an implementation of the `Clock` trait, which abstracts time handling for
`no_std` environments.

When `std` feature is enabled (which is the default case), `Clock` trait is handled
automatically from the crate internals with `std::time::SystemTime`.

### Basic Usage:

#### In `std` environments:
```rs
use timed_map::TimedMap;
use std::time::Duration;

let mut map = TimedMap::new();

map.insert_expirable(1, "expirable value", Duration::from_secs(60));
assert_eq!(map.get(&1), Some(&"expirable value"));
assert!(map.get_remaining_duration(&1).is_some());

map.insert_constant(2, "constant value");
assert_eq!(map.get(&2), Some(&"constant value"));
assert!(map.get_remaining_duration(&2).is_none());
```

#### In `no_std` environments:
```rs
use core::time::Duration;
use timed_map::{Clock, TimedMap};

struct CustomClock;

impl Clock for CustomClock {
    fn elapsed_seconds_since_creation(&self) -> u64 {
    // Hardware-specific implementation to measure the elapsed time.
        0 // placeholder
    }
}

let clock = CustomClock;
let mut map = TimedMap::new(clock);

map.insert_expirable(1, "expirable value", Duration::from_secs(60));
assert_eq!(map.get(&1), Some(&"expirable value"));
assert!(map.get_remaining_duration(&1).is_some());

map.insert_constant(2, "constant value");
assert_eq!(map.get(&2), Some(&"constant value"));
assert!(map.get_remaining_duration(&2).is_none());
```

### Advanced Usage & Tuning:

#### Customizing the Internal Map

By default, `TimedMap` uses `BTreeMap` to store data, but you can switch to `FxHashMap` or `HashMap`.

This is only available on `std` environments.

```rs
use timed_map::{MapKind, TimedMap};

let mut map = TimedMap::new_with_map_kind(MapKind::FxHashMap);
```

#### Manual Expiration Control

To have fully control over expired entries, use the `*_unchecked` functions and `drop_expired_entries` to handle expiration manually.
This can boost performance by running expiration logic only when it's necessary to maximize the performance.

```rs
let mut map = TimedMap::new();

map.insert_expirable_unchecked(1, "expirable value", Duration::from_secs(60));
assert_eq!(map.get_unchecked(&1), Some(&"expirable value"));

map.insert_constant_unchecked(2, "constant value");
assert_eq!(map.get_unchecked(&2), Some(&"constant value"));

map.drop_expired_entries();
```

#### Setting Expiration Check Frequency

In cases where inserts are frequent, `expiration_tick_cap` can be set to control how often expired entries are removed. For instance,
if there are 100 inserts per second, setting `expiration_tick_cap` to 100 will trigger the expiration check every 100 inserts which will
reduce the expiration logic overhead significantly.

```rs
use timed_map::TimedMap;

let mut map = TimedMap::new().expiration_tick_cap(100);
```