feat: implemented bigint audit in decode.ts: ensure IDs are never converted to number

[Ugasutun]

Closes #123
fix(core-ts): ensure IDs are never converted to number in decode

• Changed decodeMuxed() to return bigint instead of string for id field
• Updated parse.ts to use decoded.id directly without BigInt() conversion
• Updated routing/extract.ts to convert bigint to string only at API boundary
• Updated test expectations to use BigInt() for proper comparison

This ensures large ID values (>2^53) are never implicitly cast to JS number,
preventing precision loss in the decode pipeline.

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[codeZe-us]

@Ugasutun This is okay

[codeZe-us]

@Ugasutun resolve conflicts