Prepare sample_data for go-cart.io curated maps

[atima]

This PR:

• Added Label columns to the datasets in sample_data for use in visualization on go-cart.io curated maps.
• Updated the README to document the CSV format and new Label field.

[github-actions]

🚦 Performance Comparison ^{(α=0.05, ±5%)}

🗺️ Total maps

34

❌ Failed

0

🚀 Speed-ups

3

🐢 Slow-downs

0

⚖️ No change

31

---

❌ Failures

None 😎

🚀 Speed-ups (3)

map	main	pr	Δ %	p
belgium_​by_​region_​simplified_​since_​1995/​belgium_​population_​by_​region_​simplified_​2022.csv	0.067±0.001	0.063±0.002	-6.3	0.000
germany_​by_​state_​since_​1990/​germany_​population_​by_​state_​2011.csv	0.150±0.006	0.142±0.002	-5.0	0.002
world_​by_​region/​world_​population_​by_​region.csv	7.681±0.060	5.771±0.858	-24.9	0.003

🐢 Slow-downs (0)

none

⚖️ No significant change (31)

map	main	pr	Δ %	p
algeria_​by_​wilaya_​since_​2019/​algeria_​population_​by_​wilaya_​2022.csv	0.688±0.003	0.662±0.002	-3.8	0.000
australia_​by_​state_​and_​territory_​since_​1942/​australia_​population_​by_​state_​and_​territory_​2021.csv	0.699±0.003	0.676±0.003	-3.3	0.000
austria_​by_​state_​since_​1945/​austria_​population_​by_​state_​2020.csv	0.216±0.004	0.208±0.002	-3.9	0.000
bahamas_​by_​district_​since_​1999/​bahamas_​population_​by_​district_​2010.csv	3.254±0.039	3.144±0.014	-3.4	0.001
belgium_​by_​region_​since_​1995/​belgium_​population_​by_​region_​2022.csv	0.090±0.003	0.086±0.003	-4.0	0.004
brazil_​by_​state_​since_​1988/​brazil_​population_​by_​state_​2021.csv	0.594±0.003	0.579±0.011	-2.5	0.018
china_​by_​province_​with_​chinese_​taipei_​since_​1998/​china_​population_​by_​province_​2020.csv	0.733±0.006	0.704±0.003	-4.0	0.000
conterminous_​usa_​by_​state_​since_​1959/​conterminous_​usa_​population_​by_​state_​2020.csv	0.420±0.002	0.406±0.004	-3.3	0.000
contiguous_​usa_​by_​county_​since_​2001/​usa_​population_​by_​county_​2021.csv	30.648±3.973	31.961±5.466	+4.3	0.645
croatia_​by_​county_​since_​1992/​croatia_​covid_​cases_​by_​county_​2022.csv	0.203±0.002	0.196±0.002	-3.3	0.000
croatia_​by_​county_​since_​1992/​croatia_​population_​by_​county_​2021.csv	0.204±0.003	0.196±0.001	-3.8	0.000
egypt_​by_​governorate_​since_​2009/​egypt_​population_​by_​governate_​2017.csv	0.769±0.005	0.753±0.020	-2.1	0.107
england_​by_​region_​since_​2023/​england_​population_​by_​region_​2022.csv	1.266±0.022	1.223±0.022	-3.4	0.007
eu_​by_​country_​until_​2020/​eu_​population_​by_​country_​2021.csv	1.641±0.010	1.603±0.022	-2.3	0.007
eu_​by_​region_​until_​2020/​eu_​population_​by_​region_​2020.csv	4.986±0.040	4.891±0.026	-1.9	0.001
france_​by_​metropolitan_​region_​since_​2016/​france_​population_​by_​metropolitan_​region_​2008.csv	0.242±0.002	0.233±0.001	-3.7	0.000
indonesia_​by_​province_​since_​2022/​indonesia_​population_​by_​province_​2024.csv	0.346±0.005	0.338±0.008	-2.4	0.056
japan_​by_​prefecture_​since_​1888/​japan_​population_​by_​prefecture_​2020.csv	0.661±0.006	0.636±0.011	-3.9	0.002
malaysia_​by_​state_​since_​2001/​malaysia_​population_​by_​state_​2020.csv	0.339±0.003	0.326±0.003	-3.9	0.000
malaysia_​by_​state_​since_​2001/​malaysia_​population_​by_​state_​2020_​insetted.csv	0.298±0.002	0.291±0.007	-2.6	0.047
metropolitan_​france_​by_​departement_​since_​2015/​metropolitan_​france_​population_​by_​departement_​2022.csv	0.941±0.015	0.913±0.011	-3.0	0.004
russia_​by_​federal_​subject_​since_​2008/​russia_​population_​by_​federal_​subject_​2010.csv	1.276±0.012	1.280±0.015	+0.3	0.591
singapore_​by_​planning_​area_​since_​1999/​singapore_​population_​by_​planning_​area_​2015.csv	2.183±0.012	2.133±0.002	-2.3	0.000
switzerland_​by_​canton_​since_​1999/​switzerland_​gdp_​in_​billion_​chf_​by_​canton_​2019.csv	0.346±0.003	0.333±0.003	-3.5	0.000
switzerland_​by_​canton_​since_​1999/​switzerland_​population_​by_​canton_​2016.csv	0.299±0.002	0.290±0.003	-2.9	0.000
tunisia_​by_​governorate_​since_​1994/​tunisia_​population_​by_​governate_​2014.csv	0.325±0.003	0.313±0.001	-3.7	0.000
usa_​by_​state_​since_​1959/​usa_​population_​by_​state_​2020.csv	0.701±0.037	0.689±0.005	-1.8	0.458
usa_​by_​state_​since_​1959/​usa_​population_​by_​state_​2020_​insetted.csv	0.514±0.004	0.492±0.004	-4.2	0.000
vietnam_​by_​province_​since_​1996/​vietnam_​population_​by_​province_​2019.csv	0.648±0.004	0.626±0.006	-3.5	0.000
world_​by_​country_​since_​2022/​world_​population_​by_​country_​2010.csv	6.365±0.036	6.287±0.065	-1.2	0.033
world_​by_​region_​wo_​antarctica/​world_​population_​by_​region_​wo_​antarctica.csv	7.403±0.073	7.249±0.068	-2.1	0.004