fix(container): expose UDP ports properly

[Copilot]

What does this PR do?

Backports testcontainers-go PR #3485 to fix UDP port binding. When nat.ParsePortSpecs() processes exposed ports like "8080/udp", it creates PortBinding with empty HostPort: "". Docker interprets this as "don't bind" (port 0) rather than "bind to random port".

Modified mergePortBindings() to convert empty HostPort to "0" for automatic allocation:

// Fix: Ensure that ports with empty HostPort get "0" for automatic allocation
for k, v := range exposedPortMap {
    for i := range v {
        if v[i].HostPort == "" {
            v[i].HostPort = "0" // Tell Docker to allocate a random port
        }
    }
    exposedPortMap[k] = v
}

Before:

c, err := Run(ctx,
    WithImage("alpine/socat:latest"),
    WithExposedPorts("8080/udp"),
)
port, _ := c.MappedPort(ctx, nat.NewPort("udp", "8080"))
// port.Port() returns "0" - unusable

After:

c, err := Run(ctx,
    WithImage("alpine/socat:latest"),
    WithExposedPorts("8080/udp"),
)
port, _ := c.MappedPort(ctx, nat.NewPort("udp", "8080"))
// port.Port() returns "55051" - actual mapped port

Why is it important?

UDP services in containers were unusable - MappedPort() always returned "0" instead of the actual host port, preventing connection establishment.

Related issues

• Backports fix(udp): expose UDP ports properly testcontainers/testcontainers-go#3485

Original prompt

I want you to backport testcontainers/testcontainers-go#3485 to docker/go-sdk

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[mdelapenya]

Credits to @blueprismo

[Copilot]

Pull Request Overview

This PR backports testcontainers-go PR #3485 to fix UDP port binding. The fix addresses a bug where MappedPort() always returned "0" for UDP ports instead of the actual mapped host port, making UDP services in containers unusable.

Key changes:

• Modified mergePortBindings() to convert empty HostPort values to "0" for automatic Docker port allocation
• Updated existing test expectations in lifecycle.create_test.go to reflect the fix
• Added comprehensive test coverage for UDP port binding behavior

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
container/lifecycle.create.go	Added logic to convert empty HostPort to "0" in mergePortBindings() to enable proper port allocation
container/lifecycle.create_test.go	Updated test expectations to reflect HostPort "0" instead of empty string
container/udp_port_binding_test.go	Added comprehensive tests for UDP port binding fix and regression tests for TCP

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