Fix toolkit build and address decoding

[newmattock]

Summary:

• Fixes package compilation by using the official module path, a single shared SDKConfig, and valid Go types for variable JSON objects.
• Fixes the example import/constructor so go test ./... builds the examples package.
• Adds the Makefile targets referenced by the existing GitHub Actions workflow.
• Decodes address endpoint responses into their typed result structs and expands tests to assert decoded values.

Related bounty or issue:

• BGL (Bitgesell) Bounty/Improvement Program ($50000 budget) bitgesell#81

Baseline failure before fix:

• go test ./... failed with duplicate SDKConfig declarations, undefined object types, invalid example imports/usages, and missing transaction client fields.

Validation:

• go test ./...
• make setup && make compile
• git diff --check

Notes:

• This is a focused build and test reliability repair for the official Bitgesell Go toolkit.
• The added Makefile matches the repository's existing .github/workflows/build.yml commands.

[MyTH-zyxeon]

Review-assist note for the Bitgesell #81 improvement lane.

I checked the public PR body and diff. This looks like a build/test reliability and typed-response decoding repair for the official Go toolkit:

• switches the module/example imports to the official github.com/BitgesellOfficial/go-bitgesell-toolkit path
• removes duplicate SDKConfig declarations and replaces undefined flexible API fields with a concrete object alias
• adds the setup and compile Makefile targets used by the existing GitHub Actions workflow
• decodes address balance/transactions/UTXO responses into typed structs instead of returning empty structs
• expands address tests to assert decoded values through mocked HTTP responses

Suggested maintainer checks before merge:

• run go test ./... plus make setup && make compile
• confirm the official module path change is intended for downstream imports
• verify the address UTXO endpoint path in the mock coverage matches the live API route expected by callers
• skim the Transaction struct additions for API/data-model intent, since it now carries both client fields and JSON-mapped transaction fields

From the public patch shape, this is a meaningful #81 candidate because it turns build breakage and empty decoded results into testable behavior without requiring secrets, wallets, live nodes, or chain actions.