feat: partial key filtering for map storage queries

Problem

Currently, querying storage maps requires providing all key fields or none. There's no way to query e.g. Hrmp.HrmpChannels filtered by just sender — you must know both sender and recipient, or fetch everything.

This makes exploratory queries painful when you only know part of the key.

Proposed Solution

For NMaps (multi-hasher storage items)

polkadot-api's getEntries() natively accepts partial key prefixes. If a storage item has keys (sender, recipient), passing just (sender) returns all entries for that sender.

• Detect when fewer keys than expected are provided
• Call getEntries(partialKey) instead of getValue(fullKey)

For single-hasher maps with struct keys

These don't support partial prefix queries at the protocol level.

• Add a --filter key=value flag for client-side filtering after getEntries()
• Example: polkadot query System.Account --filter balance.free>1000000

Implementation hints

// In query command handler:
if (providedKeys.length < expectedKeys.length) {
  // Partial key — use getEntries with prefix
  const entries = await storage.getEntries(...providedKeys)
} else {
  // Full key — use getValue
  const value = await storage.getValue(...providedKeys)
}

Priority

HIGH

Files

• src/commands/query.ts
• src/commands/query.test.ts

Start in src/commands/query.ts and read the existing cases in src/commands/query.test.ts. Trace how provided keys are counted and how getValue() and getEntries() are currently used. Done means partial NMap keys query by prefix and single-hasher struct keys support the specified --filter key=value behavior, with tests covering both paths.