feat(abstract-utxo): move and reorganize UTXO coin implementations and tests

[OttoAllmendinger]

Move UTXO coin implementations from coin-specific modules into the
abstract-utxo module. Each coin implementation now resides in its own
directory under src/impl/ and is re-exported from the main module.

The original structure did not provide much benefit and makes testing much more difficult than it should be.

This change:

• Consolidates UTXO coin implementations in abstract-utxo
• Allows coin-specific modules to simply re-export implementations
• Simplifies maintenance and keeps the code DRY
• Moves test files from individual UTXO coin modules into abstract-utxo
• Reorganizes test directory structure with separate unit and integration
  test directories
• Adds sdk-test and mocha as devDependencies to abstract-utxo

This changes allows us to move the utxo tests from bitgo/test/v2/unit/coins/utxo to
abstract-utxo in subsequent PRs.

BTC-2652

[Copilot]

Pull Request Overview

This PR consolidates UTXO coin implementations by moving them from individual coin-specific modules into the abstract-utxo module, establishing a cleaner architecture where coin modules simply re-export implementations. This refactoring also relocates and reorganizes test files from individual UTXO coin modules into abstract-utxo with separate unit and integration test directories.

Key Changes:

• Moved coin implementations (BTC, BCH, BCHA, BSV, BTG, LTC, DASH, DOGE, ZEC) from sdk-coin-* modules to abstract-utxo/src/impl/
• Updated coin-specific modules to re-export from @bitgo/abstract-utxo instead of local implementations
• Reorganized test structure with dedicated unit and integration directories in abstract-utxo

Reviewed Changes

Copilot reviewed 82 out of 94 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
modules/sdk-coin-*/src/index.ts	Re-exports coin implementations from @bitgo/abstract-utxo and consolidates register function
modules/sdk-coin-*/package.json	Removes test scripts and dependencies now handled by abstract-utxo
modules/abstract-utxo/src/impl/*	New coin implementation files organized by coin type
modules/abstract-utxo/src/index.ts	Exports all coin implementations from impl directory
modules/abstract-utxo/test/*	Updated import paths to reflect new directory structure
modules/abstract-utxo/package.json	Adds devDependencies (sdk-test, mocha) and utxo-ord dependency
Dockerfile	Reorders utxo-ord module copy and linking to match dependency structure

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