refactor(config): merge test config files

[317787106]

What does this PR do?

Consolidates test configuration files by deleting four redundant config files (args-test.conf, config-test-index.conf, config-test-mainnet.conf, config-test-storagetest.conf) and standardizing tests to use a single shared config-test.conf. Also renames config-localtest.conf to config-shield.conf to better reflect its purpose (shielded-transfer tests), and removes the hardcoded seed node list from config-test.conf since unit tests have no need for P2P connectivity.

Specifically:

• Delete 4 redundant test config files (~940 lines removed)
• Rename config-localtest.conf → config-shield.conf
• Remove NET_CONF, MAINNET_CONF, LOCAL_CONF, STORAGE_CONF, INDEX_CONF from TestConstants; add SHIELD_CONF
• Update all affected test classes to reference TestConstants.TEST_CONF or TestConstants.SHIELD_CONF instead of bare string literals
• Clear seed node IPs from config-test.conf; adjust ArgsTest seed-node assertion from 11 → 0

Why are these changes required?

The previous test suite maintained five separate .conf files that largely duplicated each other, making it hard to know which config to use for a new test and causing drift over time (e.g., config-test-mainnet.conf contained mainnet genesis/seed data that is irrelevant and potentially misleading in a unit-test context). Centralizing to one default test config (config-test.conf) and one purpose-specific config (config-shield.conf) reduces maintenance overhead and eliminates accidental coupling to live-network parameters in tests.

This PR has been tested by:

• Unit Tests

Extra details

StorageTest gains additional coverage to compensate for the removal of config-test-storagetest.conf-dependent tests that were folded into the unified config.

[barbatos2011]

Follow-up observation, not blocking: although this PR deletes four redundant config files (-996 lines, well-deserved cleanup), the consolidated config-test.conf itself drops only 18 lines (387 → 369), and the renamed config-shield.conf drops 17. So the consolidation eliminates file drift risk but doesn't reduce per-test config-load surface — each of the ~21 affected tests still loads a 369-line conf, mostly boilerplate it doesn't read.

That's a real, but smaller, win. Worth being explicit in the PR description:

Note: this PR consolidates files but does not slim the unified config-test.conf (~369 lines) itself. Per-test inline overrides via ConfigFactory.parseString are a follow-up.

Otherwise reviewers (and future contributors) may expect the consolidation step alone to address the boilerplate problem, when in fact the boilerplate just got concentrated in one place.

Concrete follow-up path, if someone wants to pursue it later: tests with narrow needs (e.g. AssetUpdateHelperTest, StorageTest, ApiUtilTest) can move to inline ConfigFactory.parseString(...).withFallback(ConfigFactory.defaultReference()) and shed their dependency on TEST_CONF entirely. reference.conf already provides the safety net thanks to PR #6615.