Refactor the Context and ChainstateManager APIs to use functional options

[stringintech]

This PR refactors the Context and ChainstateManager APIs to use functional options that work directly with raw C option pointers, removing the Go wrapper structs ContextOptions and ChainstateManagerOptions.

This simplification:

• Reduces API surface area by eliminating intermediate wrapper types
• Follows idiomatic Go functional options pattern

Context API

Previous approach:

// Create chain parameters
chainParams, err := NewChainParameters(ChainTypeRegtest)
if err != nil {
    return err
}
defer chainParams.Destroy()

// Create options struct
opts := NewContextOptions()
opts.SetChainParams(chainParams)
opts.SetNotifications(notificationCallbacks)
opts.SetValidationInterface(validationCallbacks)
defer opts.Destroy()

// Create context from options
ctx, err := NewContext(opts)

New approach:

// Create context with functional options directly
ctx, err := NewContext(
    WithChainType(ChainTypeRegtest),
    WithNotifications(notificationCallbacks),
    WithValidationInterface(validationCallbacks),
)

ChainstateManager API

Previous approach:

// Create options struct
opts, err := NewChainstateManagerOptions(ctx, dataDir, blocksDir)
if err != nil {
    return err
}
defer opts.Destroy()

opts.SetWorkerThreads(1)
opts.UpdateBlockTreeDBInMemory(true)
opts.UpdateChainstateDBInMemory(true)
err = opts.SetWipeDBs(true, true)
if err != nil {
    return err
}

// Create chainstate manager from options
manager, err := NewChainstateManager(opts)

New approach:

// Create chainstate manager with functional options directly
manager, err := NewChainstateManager(ctx, dataDir, blocksDir,
    WithWorkerThreads(1),
    WithBlockTreeDBInMemory,
    WithChainstateDBInMemory,
    WithWipeDBs(true, true),
)