fix: guard RpcDataSource against invalid decimals to prevent NaN bala…

[salimtb]

…nces

Two fixes that together stop entries like
eip155:4326/erc20:0x000…000: { amount: "NaN" } from leaking into assetsBalance.

• #collectMetadataForBalances: only reuse existing native metadata when it has finite decimals (via new #hasValidDecimals helper). Empty name/symbol are still accepted, and decimals: 0 is valid. Bad state metadata (e.g. { decimals: null, name: '', symbol: '', type: 'native' }) is replaced by the chain-status stub so the pipeline resolves a usable decimals.

• #convertToHumanReadable: defensively return '0' when decimals isn't a finite non-negative number or when rawBalance can't be parsed. Defaulting decimals to a fixed value (e.g. 18) would silently produce wrong amounts; '0' matches the existing safe fallback used in the error path.

Adds 7 tests covering the bug payload (decimals: null), NaN decimals, negative decimals, non-numeric raw balance, and the decimals: 0 / missing name/symbol valid cases.

Explanation

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Touches balance formatting and native metadata selection in RpcDataSource, which can affect emitted assetsBalance/assetsInfo values across chains and accounts. Changes are defensive and well-tested but could alter behavior for edge-case metadata payloads.

Overview
Prevents RpcDataSource from emitting { amount: "NaN" } (or silently wrong '0') balances when native asset metadata in state contains invalid decimals.

Native metadata reuse is now gated by a new #hasValidDecimals (finite, non-negative; 0 allowed), otherwise falling back to the chain-status stub, and decimals selection no longer uses ??—a new #pickValidDecimals skips NaN/negative values so stale state can’t shadow valid pipeline metadata.

#convertToHumanReadable now returns '0' when decimals is invalid or the raw balance is unparsable, and the PR adds focused unit tests covering null/NaN/negative decimals and invalid raw balances (plus valid decimals: 0 cases).

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