CMM-1202 create the stats country endpoint

[adalpari]

Summary

• Add new stats/country-views endpoint for WordPress.com REST API v1.1
• Returns location/country-based view statistics with support for both summary and per-day breakdown modes
• All response fields support null values for robust API handling

Changes

New files:

• wp_api/src/wp_com/stats_country_views.rs - Type definitions and parameters
• wp_api/src/wp_com/endpoint/stats_country_views_endpoint.rs - Endpoint implementation
• wp_api/tests/wpcom/stats_country_views/*.json - Test fixtures for parameterized tests

Types added:

• StatsCountryViewsPeriod - Period enum (day, week, month, year)
• StatsCountryViewsParams - Query parameters (period, date, start_date, max, num, days, locale, summarize)
• StatsCountryViewsResponse - Response with summary or days depending on summarize parameter
• StatsCountryInfo - Country metadata (flag icons, country name, map region)
• StatsCountryView - Individual country view entry (location, views, country_code)

Response modes:

• summarize=0 (default): Returns days field with per-day breakdown keyed by date
• summarize=1: Returns summary field with aggregated country views

Test plan

• Unit tests for parameter serialization
• Parameterized tests for JSON deserialization covering summary, days, null values, and empty responses
• Lint passes (cargo fmt, cargo clippy)

[adalpari]

@jkmassel I added the remaining stuff to this endpoint:

• WPComLanguage
• Renaming and parametrizing json deserialization tests
• e2e test

[jkmassel]

We should match the endpoints from the last PR – if we think this should be true by default we should have it be default=true and remove the optionality.

[adalpari]

Ahh, I forgot about this 🤦
Done

[jkmassel]

Does this need to be its own test?

It seems to be mostly covered by the test above – should we add more parameters to it?

[adalpari]

There's a small difference between these tests. The above one is a lightweight sanity check test for general purposes (parameterised), while this one is more about checking the detailed values. Si, it's not only checking the deserialisation, but checking that the expected values are present.
Hence, I think that both tests add value in their way. Plus, I think that having extra tests is harmless.

Does it make sense?

[jkmassel]

I agree it's not hurting anything, so I'm fine to leave it :)