timer.Start calls timer.tick() too frequently

**Describe the bug**
The timer package's documentation does not accurately describe the actual behavior of the timer.

**Setup**
N/A

**To Reproduce**
```golang

t := timer.New(5 * time.Second)

t.Start()
t.Start() // According to documentation, this second start should have no effect

time.Sleep(time.Second + delta) // Just for demo purposes

fmt.Println(t.Timeout) // 3 * time.Second
```

**Source Code**
`timer.startStop` fires off a `StartStopMsg` message which in turn causes `timer.Update` to enqueue `timer.tick`. `timer.tick` in turn enqueues `TickMsg`. `timer.Update` assumes each tick is fired at exact intervals; therefore, calling `timer.tick` multiple times artificially speeds up the timer.

[CS](https://github.com/charmbracelet/bubbles/blob/ff8b5a8e17c91972211d0b9f03e7764ddaa2f6d0/timer/timer.go#L150)

**Expected behavior**
See [documentation](https://pkg.go.dev/github.com/charmbracelet/bubbles/timer#Model.Start), which states calling `timer.Start` multiple times will have no effect. This is the expected behavior for a normal developer, but is not what actually happens.

A suggested fix will be to record the time of the last time a `TickMsg` message has been processed in `timer.Update` and subtract the duration (recommended in any case), **or** do not issue a `StartStopMsg` when `timer.running` matches the `startStop` input.

**Screenshots**
N/A

**Additional context**
The example suggested `reset` functionality as described in the example [CS](https://github.com/charmbracelet/bubbletea/blob/f9233d51192293dadda7184a4de347738606c328/examples/timer/main.go#L57) is also inaccurate. This assumes the timer is already in the run state and does nothing if the timer has already stopped.