fix(ssa): Do not generate apply functions when no lambda variants exist

[vezenovm]

Description

Problem*

Resolves #8543

As per the issue, if there are no lambda variants we will simply panic during defunctionalize:

        assert!(
            !variants.is_empty(),
            "ICE: at least one variant should exist for a dynamic call {signature:?}"
        );

Summary*

If a function is declared but never called we can simply not generate any code for it. We do not require a variant to continue compilation. No variants for a lambda parameter essentially means that the function was never called and this should not prevent us for completing compilation. The unused parameter can then be removed during DIE pruning of dead parameters (right now we prevent pruning function parameters although this can be updated to only not remove entry point parameters).

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'Compilation Time'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.20.

Benchmark suite	Current: 7d031de	Previous: 4972733	Ratio
rollup-base-public	16.22 s	12.36 s	1.31

This comment was automatically generated by workflow using github-action-benchmark.

CC: @TomAFrench