docs: add hints for go fix tool

[phm07]

This PR adds //go:fix inline hints to compatible deprecated functions. This makes it possible for the go fix tool to automatically replace deprecated members with their recommended alternative.

Example

Before

func foo() {
	client := hcloud.NewClient(hcloud.WithBackoffFunc(hcloud.ConstantBackoff(5 * time.Second)))
	client = hcloud.NewClient(hcloud.WithPollBackoffFunc(hcloud.ExponentialBackoff(2.0, 2)))
	client = hcloud.NewClient(hcloud.WithPollInterval(5 * time.Second))

	_, _ = client.Action.All(context.Background())

	floatingIP := &hcloud.FloatingIP{ID: 123}
	_ = floatingIP.DNSPtrForIP(net.IP{})

	_ = hcloud.String("abc")
	_ = hcloud.Duration(time.Second)
	_ = hcloud.Int(123)
	_ = hcloud.Bool(true)

	var err hcloud.Error
	if err.Code == hcloud.ErrorCodeLimitReached {
		/* ... */
	}

	var (
		_ hcloud.PrimaryIPAssignResult
		_ hcloud.PrimaryIPChangeDNSPtrResult
		_ hcloud.PrimaryIPChangeProtectionResult
	)
}

After go fix

func foo() {
	client := hcloud.NewClient(hcloud.WithRetryOpts(hcloud.RetryOpts{BackoffFunc: hcloud.ConstantBackoff(5 * time.Second)}))
	client = hcloud.NewClient(hcloud.WithPollOpts(hcloud.PollOpts{BackoffFunc: hcloud.ExponentialBackoff(2.0, 2)}))
	client = hcloud.NewClient(hcloud.WithPollOpts(hcloud.PollOpts{BackoffFunc: hcloud.ConstantBackoff(5 * time.Second)}))

	_, _ = client.Action.AllWithOpts(context.Background(), hcloud.ActionListOpts{ID: []int64{}})

	floatingIP := &hcloud.FloatingIP{ID: 123}
	_ = hcloud.IgnoreError(floatingIP.GetDNSPtrForIP(net.IP{}))

	_ = hcloud.Ptr("abc")
	_ = hcloud.Ptr(time.Second)
	_ = hcloud.Ptr(123)
	_ = hcloud.Ptr(true)

	var err hcloud.Error
	if err.Code == hcloud.ErrorCodeRateLimitExceeded {
		/* ... */
	}

	var (
		_ schema.PrimaryIPActionAssignResponse
		_ schema.PrimaryIPActionChangeDNSPtrResponse
		_ schema.PrimaryIPActionChangeProtectionResponse
	)
}

[codecov]

Codecov Report

❌ Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.29%. Comparing base (5bb7ba6) to head (f6c3b95).

Files with missing lines	Patch %	Lines
hcloud/client.go	0.00%	3 Missing ⚠️
hcloud/helper.go	0.00%	2 Missing ⚠️
hcloud/action.go	0.00%	1 Missing ⚠️
hcloud/floating_ip.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #849      +/-   ##
==========================================
- Coverage   78.39%   78.29%   -0.10%     
==========================================
  Files          60       60              
  Lines        4355     4358       +3     
==========================================
- Hits         3414     3412       -2     
- Misses        637      642       +5     
  Partials      304      304              

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[phm07]

I added ID: []int64{} explicitly here to make clear that a list of IDs is expected. This function should have been broken for over a year anyway.

[phm07]

This helper is necessary to make it possible to inline (*FloatingIP).DNSPtrForIP. If we don't want to export it we could consider moving it to exp/ (though there would be an import cycle if we moved it to errutil) or removing it entirely.