Release v3.5.2: version bump + CHANGELOG reconciliation

Bump version 3.5.1 -> 3.5.2 across __init__.py, pyproject.toml,
rust/Cargo.toml, llms-full.txt, and CITATION.cff (date-released
2026-06-08).

Reconcile the CHANGELOG: the Firpo & Possebom (2018) confidence-sets
-by-test-inversion feature (PR #527) was filed under [3.5.1] but
merged AFTER the v3.5.1 tag was cut, so the tagged v3.5.1 did not
actually contain it. Move that entry into the new [3.5.2] section
alongside everything else that landed post-tag (CBWSDID balancing
#534, SyntheticControl conformal inference #530, the
placebo_effects -> variance_effects rename/deprecation #532, and the
ImputationDiD validation + SE fixes #533). The Firpo PR-A paper
review (#524, docs-only) stays in [3.5.1] since it was in that tag.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: igerber

CHANGELOG.md

@@ -7,8 +7,8 @@ authors:
     family-names: Gerber
     orcid: "https://orcid.org/0009-0009-3275-5591"
 license: MIT
-version: "3.5.1"
-date-released: "2026-06-02"
+version: "3.5.2"
+date-released: "2026-06-08"
 doi: "10.5281/zenodo.19646175"
 url: "https://github.com/igerber/diff-diff"
 repository-code: "https://github.com/igerber/diff-diff"

CITATION.cff

@@ -298,7 +298,7 @@
 DCDH = ChaisemartinDHaultfoeuille
 HAD = HeterogeneousAdoptionDiD
 
-__version__ = "3.5.1"
+__version__ = "3.5.2"
 __all__ = [
     # Estimators
     "DifferenceInDifferences",

diff_diff/__init__.py

@@ -2,7 +2,7 @@
 
 > A Python library for Difference-in-Differences causal inference analysis. Provides sklearn-like estimators with statsmodels-style output for econometric analysis.
 
-- Version: 3.5.1
+- Version: 3.5.2
 - Repository: https://github.com/igerber/diff-diff
 - License: MIT
 - Dependencies: numpy, pandas, scipy (no statsmodels dependency)

diff_diff/guides/llms-full.txt

@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "diff-diff"
-version = "3.5.1"
+version = "3.5.2"
 description = "Difference-in-Differences causal inference with sklearn-like API. Callaway-Sant'Anna, Synthetic DiD, Honest DiD, event studies, parallel trends."
 readme = "README.md"
 license = "MIT"

pyproject.toml

@@ -1,6 +1,6 @@
 [package]
 name = "diff_diff_rust"
-version = "3.5.1"
+version = "3.5.2"
 edition = "2021"
 rust-version = "1.85"
 description = "Rust backend for diff-diff DiD library"