Test parameter description punctuation, fix 178 violations (#340) (#1664)

Adds `policyengine_uk/tests/test_parameter_descriptions.py` which asserts
every parameter `description` ends with a period — and brings the existing
178 parameter files into compliance. Multi-line descriptions are handled
by appending the period to the last continuation line so the sentence ends
correctly when YAML joins them.

Per #339, these descriptions surface in the UI and were inconsistent;
locking the convention in CI prevents drift going forward.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: vahid-ahmadi

changelog.d/340.md

@@ -1,4 +1,4 @@
-description: Most recent September CPIH index value, updated for each uprating occurrence (2005=100)
+description: Most recent September CPIH index value, updated for each uprating occurrence (2005=100).
 values:
   2005-01-01: 100
   2010-01-01: 114.48

policyengine_uk/parameters/gov/benefit_uprating_cpi.yaml

@@ -1,4 +1,4 @@
-description: Bank of England base rate
+description: Bank of England base rate.
 metadata:
   label: BoE base rate
   unit: /1

policyengine_uk/parameters/gov/boe/base_rate.yaml

@@ -1,4 +1,4 @@
-description: Household income limit for Adult Dependants' Grant
+description: Household income limit for Adult Dependants' Grant.
 metadata:
   label: Adult Dependants' Grant household income limit
   unit: currency-GBP

policyengine_uk/parameters/gov/dfe/adult_dependants_grant/income_limit.yaml

@@ -1,4 +1,4 @@
-description: Maximum Adult Dependants' Grant amount
+description: Maximum Adult Dependants' Grant amount.
 metadata:
   label: Adult Dependants' Grant maximum
   unit: currency-GBP

policyengine_uk/parameters/gov/dfe/adult_dependants_grant/maximum.yaml

@@ -1,4 +1,4 @@
-description: Income limit for a non-partner adult dependant in the Adult Dependants' Grant assessment
+description: Income limit for a non-partner adult dependant in the Adult Dependants' Grant assessment.
 metadata:
   label: Adult Dependants' Grant other adult income limit
   unit: currency-GBP

policyengine_uk/parameters/gov/dfe/adult_dependants_grant/other_adult_income_limit.yaml

@@ -1,4 +1,4 @@
-description: Minimum age for Employment and Support Allowance
+description: Minimum age for Employment and Support Allowance.
 metadata:
   unit: year
   period: year

policyengine_uk/parameters/gov/dwp/ESA/eligibility/min_age.yaml

@@ -1,5 +1,5 @@
 description: Income-based Employment and Support Allowance personal allowance for
-  persons aged 18-24
+  persons aged 18-24.
 metadata:
   economy: false
   period: week

policyengine_uk/parameters/gov/dwp/ESA/income/amount_18_24.yaml

@@ -1,5 +1,5 @@
 description: Income-based Employment and Support Allowance personal allowance for
-  persons aged over 25
+  persons aged over 25.
 metadata:
   economy: false
   period: week

policyengine_uk/parameters/gov/dwp/ESA/income/amount_over_25.yaml

@@ -1,5 +1,5 @@
 description: Income-based Employment and Support Allowance personal allowance for
-  couples
+  couples.
 metadata:
   economy: false
   period: week