refactor(config): remove unused storage index and json parsing config

[317787106]

What does this PR do?

Removes two groups of unused or over-engineered config items:

1. node.http.maxNestingDepth / node.http.maxTokenCount — these are JSON-parsing DoS-protection caps that were exposed as user-configurable fields in reference.conf, NodeConfig.HttpConfig, and CommonParameter. Because the values were baked into the JSON / JsonRpcServlet class-level ObjectMapper at first class-load, exposing them as runtime config created a silent initialization-order trap: if any code touched JSON before Args.setParam() completed, the user's overrides would be silently ignored. The values (100 / 100 000) are security constants, not operator-tunable settings. This PR promotes them to Constant.MAX_NESTING_DEPTH / Constant.MAX_TOKEN_COUNT, removes the config binding, and deletes the fragile init-order comment that described the footgun.

2. storage.index.directory / storage.index.switch — legacy config keys that have no consumers in runtime code. Storage.indexDirectory and Storage.indexSwitch were populated from config but never read. The StorageConfig.IndexConfig inner class and all config/field bindings are removed. The corresponding CLI flags (--storage-index-directory, --storage-index-switch) retain their @Parameter declarations so JCommander still recognises them — preventing a misleading startup crash for operators whose launch scripts still pass these flags — but the values are no longer applied anywhere.

Why are these changes required?

• Removing dead config items reduces cognitive overhead for operators reading reference.conf and for developers maintaining the config-binding pipeline.
• Eliminating the CommonParameter-backed maxNestingDepth/maxTokenCount fields removes a class-initialization ordering constraint that was documented only in a comment, making startup order more robust and the JSON utility class simpler.
• Keeping the CLI flag declarations (without bindings) avoids a hard startup break: without them, JCommander treats unknown flags as positional seed-node arguments, causing a misleading Invalid inetSocketAddress crash with no indication that the flag was removed.
• Aligns with the ongoing effort to trim CommonParameter and reference.conf of accumulated legacy fields (part of the feature/reduce_482_config series).

This PR has been tested by:

• Unit Tests (StorageConfigTest, ArgsTest, JsonTest, JsonRpcServletTest updated/passing)
• Verified that nodes started with --storage-index-directory / --storage-index-switch still start normally and emit a deprecation warning instead of crashing

Follow up

Continue auditing CommonParameter and reference.conf for additional unused or redundant config entries.

Extra details

No behaviour change for any running node: the JSON depth/token limits remain exactly 100 / 100 000; index storage was already a no-op. Operators passing the removed index CLI flags get a deprecation warning on startup; the flags are silently consumed and ignored.