feat: Add partial support for PAR auth flow

[pmathew92]

Changes

Ports the Pushed Authorization Request (PAR) flow from main (3.x) to v4_development. In this flow the backend-for-frontend (BFF) handles the /oauth/par and /oauth/token endpoints while the SDK manages the browser-based authorization and returns the authorization code.

• New WebAuthProvider.authorizeWithRequestUri(account) entry point returning a PARBuilder (start / await / withCustomTabsOptions / withSessionTransferToken).
• New PARCodeManager, PARCodeManagerState, PARUtils, AuthorizeResultParser, and AuthorizationCode result type.
• WebAuthProvider save/restore instance state extended to cover the PAR manager.

Usage

// Callback style
WebAuthProvider.authorizeWithRequestUri(account)
    .start(context, requestUri, object : Callback<AuthorizationCode, AuthenticationException> {
        override fun onSuccess(result: AuthorizationCode) {
            // Exchange result.code for tokens via BFF
        }
        override fun onFailure(error: AuthenticationException) {
            // Handle error
        }
    })

// Coroutines
val authCode = WebAuthProvider.authorizeWithRequestUri(account)
    .await(context, requestUri)
// Exchange authCode.code for tokens via BFF

v4 adaptations

• Test imports converted from com.nhaarman.mockitokotlin2.* to org.mockito.kotlin.* (v4 convention).
• EXAMPLES.md PAR section uses ## headings to match v4's sibling sections (## Native to Web SSO login, ## DPoP).

Testing

• This change adds unit test coverage (PARCodeManagerTest, plus 5 PAR cases in WebAuthProviderTest).

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