refactor: replace string concatenation in monitor CLI option construc…

[singhshresth26]

Description

This PR refactors the monitor/hypervisor command line arguments construction to use string slices directly instead of inefficient string concatenation.

Previously, monitors (such as HVT, SPT, QEMU, Firecracker, and Cloud Hypervisor) built their CLI options as a single space-separated string using cli += " option" and split it into a string slice at the end using strings.Split. This is inefficient because strings are immutable in Go, leading to unnecessary memory allocations, and the split operation adds overhead.

This PR:

• Updates the Unikernel interface method MonitorNetCli to return []string instead of string.
• Updates MonitorBlockArgs.ExactArgs and MonitorCliArgs.OtherArgs to use []string instead of string.
• Updates all hypervisors to construct their arguments directly as slices of strings, avoiding all string concatenations and subsequent splits.

Related issues

• Fixes Replace the string concatenation in the monitor command line construction #844

How was this tested?

Compiled the packages and verified that unit tests build successfully targeting Linux:

• go build ./pkg/unikontainers/... - Passed successfully.
• go test -c ./pkg/unikontainers/... - Passed successfully.

Checklist

• I have read the contribution guide.
• The linter passes locally (make lint).
• The e2e tests of at least one tool pass locally (make test_ctr, make test_nerdctl, make test_docker, make test_crictl).
• If LLMs were used: I have read the llm policy.

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