Add base::expected<>-style API to the "fetch balance" flow

[Miyayes]

Most important is balance related.

[Miyayes]

@szilardszaloki Would you be able to rename this issue to something more specific, now that you made some definite changes? :)

[kjozwiak]

The above requires 1.50.94 or higher for 1.50.x verification 👍

[LaurenWags]

Verified with

Brave | 1.50.102 Chromium: 111.0.5563.116 (Official Build) beta (x86_64)
-- | --
Revision | ade86b9472831e26d87fd569e04b404be01e1e2b-refs/branch-heads/5563@{#1209}
OS | macOS Version 12.6.3 (Build 21G419)

• Verified the test plan from Introduces FetchBalanceResult. brave-core#17480 (comment)

1. Before enabling rewards - PASSED

• Confirmed that there is no Balance info displayed on the brave://rewards-internals page before enabling the rewards

2. After enabling rewards - PASSED

• Confirmed that after enabling the rewards the vBAT balance is shown on the Rewards Internals page
• Confirmed that the Connect account is shown on the brave://rewards settings page, BR panel and rewards NTP widget

Example	Example	Example	Example

3. After connecting a custodial wallet - PASSED

• Confirmed that after connecting custodian wallet, both the vBAT/external wallet balance is displayed on the Rewards Internals page
• Confirmed that after connecting custodian wallet, total balance is displayed on the Rewards page, Rewards panel and Rewards NTP widget

Example	Example	Example	Example

4. Logged out state - PASSED

• Confirmed that in the logged out state,the vBAT balanceis shown only on the Rewards Internals page
• Confirmed that Logged out UI is shown on the brave://rewards, BR panel, Rewards NTP and Tipping banner
• Confirmed that : ( You are currently logged out text message is shown on the tipping banner

Example	Example	Example	Example	Example

5. Fail the fetch balance request - PASSED

• Uphold wallet (pre-req: have Charles Proxy set up to return 500 error for the endpoint (https://api-sandbox.uphold.com/v0/me/cards/*)
• Confirmed that spinner animation is shown for both the Rewards BAT (vBAT) and external wallet balance on brave://rewards-internals page

Example	Example	Example	Example

6. Reset rewards - PASSED

• Confirmed that after Reset rewards the wallet balance info is not displayed on the brave://rewards-internals page

[GeetaSarvadnya]

Verification PASSED on Samsung Galaxy version 12 running Bravemonoarm64.apk_1.50.101

• Verified the test plan from Introduces FetchBalanceResult. brave-core#17480 (comment)

1. Before enabling rewards - PASSED

• Confirmed that there is no Balance info displayed on the brave://rewards-internals page before enabling the rewards

2. After enabling rewards - PASSED

• Confirmed that after enabling the rewards the vBAT balance is shown on the Rewards Internals page
• Confirmed that the Connect account is shown on the brave://rewards settings page, BR panel and rewards NTP widget (NA)

Example	Example	Example

3. After connecting a custodial wallet - PASSED

• Confirmed that after connecting custodian wallet, both the vBAT/external wallet balance is displayed on the Rewards Internals page
• Confirmed that after connecting custodian wallet, total balance is displayed on the Rewards page, Rewards panel and Rewards NTP widget (NA)

Example	Example	Example

4. Logged out state - logged #29361

• Confirmed that in the logged out state,the vBAT balanceis shown only on the Rewards Internals page
• Confirmed that Logged out UI is shown on the brave://rewards, BR panel, Rewards NTP (NA) and Tipping banner
• Confirmed that : ( You are currently logged out text message is shown on the tipping banner, logged [Android] In logged out state, the text message : ( You are currently logged out is NOT displayed on the tipping banner  #29361

Example	Example	Example	Example

5. Fail the fetch balance request - PASSED

• Uphold wallet (pre-req: have Charles Proxy set up to return 500 error for the endpoint (https://api-sandbox.uphold.com/v0/me/cards/*)
• Confirmed that spinner animation is shown for both the Rewards BAT (vBAT) and external wallet balance on brave://rewards-internals page, encountered [Android] Loading... spinner animation is NOT shown in the BR panel when rewards custodian is failed to fetch the balance #29054

Example	Example	Example

6. Reset rewards - PASSED

• Confirmed that after Reset rewards the wallet balance info is not displayed on the brave://rewards-internals page

Example	Example