[Bug]: PaymentCurrencyAmount.value type is inconsistent with W3C Payment Request API spec

[dinstein]

What happened?

Description

The value field in PaymentCurrencyAmount is currently defined as a numeric type (float in Python, float64 in Go, Double in Kotlin), but the W3C Payment Request API specification defines it as a DOMString (string type).

This inconsistency may cause issues with cross-language interoperability and deviates from the standard that the codebase explicitly references in its docstrings.

Affected files

• src/ap2/types/payment_request.py — value: float
• samples/go/pkg/ap2/types/payment_request.go — Value float64
• samples/android/.../data/ShoppingAgentTypes.kt — val value: Double

Proposed fix

Change value to a string type across all languages to align with the W3C spec.

See PR: #191

Relevant log output

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