Support #if/#elseif/#endif conditional compilation in mock generation

[DominatorVbN]

Summary

Fixes #471 — conditional compilation blocks (#if/#elseif/#else/#endif) in protocols and classes are now correctly handled by the mock generator.

• Uses SwiftIfConfig (already included in the swift-syntax package dependency) to evaluate #if conditions against a configurable build configuration.
• Replaces the // TODO: Implement #if functionality. stub in Crawler.visit(_:IfConfigDeclSyntax) with proper active-clause evaluation — only the active branch's members are crawled.
• Adds a new build_conditions field to Cuckoofile.toml module configuration so users can declare which custom conditions are active during mock generation:

[modules.MyModule]
sources = ["Sources/**/*.swift"]
output = "GeneratedMocks.swift"
build_conditions = ["DEBUG", "MY_FEATURE_FLAG"]

• Platform/OS/arch/runtime conditions that can't be known at generation time (e.g. os(iOS)) default to false (inactive), matching the safest behaviour — only explicitly declared conditions are active.

Changes

File	Change
Package.swift	Add SwiftIfConfig product to CuckooGenerator target dependencies
Generator/Project.swift	Mirror the same dependency for the Tuist project
Generator/Sources/Internal/Crawlers/CuckooGeneratorBuildConfiguration.swift	New — implements BuildConfiguration protocol for use with SwiftIfConfig
Generator/Sources/Internal/Crawlers/Crawler.swift	Use SwiftIfConfig to evaluate #if conditions; propagate buildConfiguration through sub-crawlers
Generator/Sources/CLI/Module.swift	Add buildConditions: Set<String> property and build_conditions TOML key
Generator/Sources/CLI/Generator.swift	Construct CuckooGeneratorBuildConfiguration from module's buildConditions and pass to Crawler.crawl

Test plan

• Protocol with #if MY_FLAG block: when MY_FLAG is in build_conditions, the flagged methods appear in the generated mock; when absent, they are excluded
• #elseif and #else branches are resolved to the correct active clause
• Nested #if blocks inside #if blocks work correctly
• Platform conditions like #if os(iOS) produce no members by default (not crashing or including both branches)
• Existing mocks without any #if blocks are unaffected