Remove panic from GTU7 constructor and add documentation

[Copilot]

The NewGTU7 constructor panicked on serial port errors and lacked documentation.

Changes:

• Deferred serial port initialization to Run() – Constructor now cannot fail, matching patterns used by LED, BME280, and VH400 devices
• Added godoc – Documents parameters, behavior, and test injection via cfg.Reader
• Refactored struct – Stores GTU7Config directly instead of extracted fields

Before:

func NewGTU7(cfg GTU7Config) *GTU7 {
    port, err := cfg.Factory.OpenSerial(cfg.Serial)
    if err != nil {
        panic(err)  // Constructor can crash
    }
    return &GTU7{name: cfg.Name, r: port, ...}
}

After:

// NewGTU7 constructs a GTU7 GPS sensor with the given configuration.
//
// The GTU7 reads NMEA 0183 sentences (GPGGA, GPRMC, GPVTG) from a serial port
// and emits GPSFix updates. Serial port initialization is deferred to Run(),
// so this constructor cannot fail.
func NewGTU7(cfg GTU7Config) *GTU7 {
    return &GTU7{cfg: cfg, out: make(chan GPSFix, 4)}
}

func (g *GTU7) Run(ctx context.Context) error {
    port, err := g.cfg.Factory.OpenSerial(g.cfg.Serial)
    if err != nil {
        return err  // Proper error handling
    }
    defer func() { _ = port.Close() }()
    // ...
}

---

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• go.googlesource.com
  • Triggering command: /update-job-proxy /update-job-proxy fips140/mlkem (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy -o br-131449314c26 -j DROP Trust_ECC_Root-0-n1 /opt/hostedtoolc--format=format:%H %ct %D test ba47f30cb112e8e8git /tmp/go-build201config e3f28caf test -e ommScope_Public_Trust_RSA_Root-02.pem ache/go/1.24.11/x64/pkg/tool/linux_amd64/vet /usr/bin/test --noprofile ux_amd64/compile--wait it test (dns block)
• gopkg.in
  • Triggering command: /update-job-proxy /update-job-proxy fips140/mlkem (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy -o br-131449314c26 -j DROP Trust_ECC_Root-0-n1 /opt/hostedtoolc--format=format:%H %ct %D test ba47f30cb112e8e8git /tmp/go-build201config e3f28caf test -e ommScope_Public_Trust_RSA_Root-02.pem ache/go/1.24.11/x64/pkg/tool/linux_amd64/vet /usr/bin/test --noprofile ux_amd64/compile--wait it test (dns block)
• periph.io
  • Triggering command: /update-job-proxy /update-job-proxy fips140/mlkem (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy -o br-131449314c26 -j DROP Trust_ECC_Root-0-n1 /opt/hostedtoolc--format=format:%H %ct %D test ba47f30cb112e8e8git /tmp/go-build201config e3f28caf test -e ommScope_Public_Trust_RSA_Root-02.pem ache/go/1.24.11/x64/pkg/tool/linux_amd64/vet /usr/bin/test --noprofile ux_amd64/compile--wait it test (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)