Add test coverage for serial driver implementation

[Copilot]

The serial driver implementation (drivers/serial_linux.go) lacked test coverage for critical low-level logic including termios configuration, baud rate mapping, and file descriptor management.

Changes

drivers/serial_test.go - Platform-agnostic validation tests:

• Configuration validation (empty port, zero/negative baud rates)
• Zero value behavior
• Edge case handling with table-driven tests

drivers/serial_linux_test.go - Linux-specific driver tests:

• Baud rate to Unix constant conversion for all 6 supported rates (4800-115200)
• Unsupported baud rate error handling
• Interface compliance verification
• Invalid configuration rejection

All tests are hermetic (no hardware interaction) and follow repository patterns (testify assertions, parallel execution, table-driven where applicable).

// Example: baud rate conversion testing
func TestBaudToUnix(t *testing.T) {
    tests := []struct {
        baud     int
        expected uint32
        wantErr  bool
    }{
        {9600, unix.B9600, false},
        {115200, unix.B115200, false},
        {230400, 0, true}, // unsupported
    }
    // ...
}

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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

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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 ions =0 ux_amd64/link go_.�� x64/src/net ache/go/1.24.11/-ifaceassert /bin/java -p internal/nettracrev-parse -lang=go1.24 /bin/java -o b:/usr/lib -trimpath nfig/composer/vendor/bin/as -p compress/flate -lang=go1.24 (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy -o br-18712d6c44f9 -j DROP ertum_EC-384_CA.pem eroutfiles.txt test s/drivers/ads111git s/drivers/doc.go-c s/drivers/gpiocdlog.showsignature=false test -e 2888f65.0 s/drivers/vpio_f--format=format:%H %ct %D /usr/bin/test -v ication_Authorit--wait ache/go/1.24.11/-t test (dns block)
• gopkg.in
  • Triggering command: /update-job-proxy /update-job-proxy ions =0 ux_amd64/link go_.�� x64/src/net ache/go/1.24.11/-ifaceassert /bin/java -p internal/nettracrev-parse -lang=go1.24 /bin/java -o b:/usr/lib -trimpath nfig/composer/vendor/bin/as -p compress/flate -lang=go1.24 (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy -o br-18712d6c44f9 -j DROP ertum_EC-384_CA.pem eroutfiles.txt test s/drivers/ads111git s/drivers/doc.go-c s/drivers/gpiocdlog.showsignature=false test -e 2888f65.0 s/drivers/vpio_f--format=format:%H %ct %D /usr/bin/test -v ication_Authorit--wait ache/go/1.24.11/-t test (dns block)
• periph.io
  • Triggering command: /update-job-proxy /update-job-proxy ions =0 ux_amd64/link go_.�� x64/src/net ache/go/1.24.11/-ifaceassert /bin/java -p internal/nettracrev-parse -lang=go1.24 /bin/java -o b:/usr/lib -trimpath nfig/composer/vendor/bin/as -p compress/flate -lang=go1.24 (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy -o br-18712d6c44f9 -j DROP ertum_EC-384_CA.pem eroutfiles.txt test s/drivers/ads111git s/drivers/doc.go-c s/drivers/gpiocdlog.showsignature=false test -e 2888f65.0 s/drivers/vpio_f--format=format:%H %ct %D /usr/bin/test -v ication_Authorit--wait ache/go/1.24.11/-t test (dns block)

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