Bump version to 3.6.1 (#593)

Release 3.6.1. Changes since 3.6.0:
- LPDiD non-absorbing (reversible) treatment with entry-effect estimands
  (Dube, Girardi, Jorda & Taylor 2025) + complex-survey-design support
  (survey_design=), each R-parity validated.
- TROP non-absorbing (on/off) treatment support, opt-in local method
  (Athey, Imbens, Qu & Viviano 2025).
- Weighted multiple absorbed fixed effects (absorb=[a, b, ...]) via
  iterative alternating-projection demeaning.
- CallawaySantAnna materializes non-estimable (g,t) cells as NaN.
- Fix: BusinessReport appendix render failures now surfaced.
- R-parity validation backfill for the LPDiD absorbing/non-absorbing/survey
  paths; survey zero-weight-PSU SE-invariance item waived (Lumley
  full-design convention); SciPy lower-bound doc alignment.

Promotes the CHANGELOG [Unreleased] section to [3.6.1] - 2026-07-01 and
syncs the version across __init__.py, pyproject.toml, rust/Cargo.toml,
llms-full.txt, and CITATION.cff.

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

Bump version to 3.6.0 (#581)

Release 3.6.0. Highlights since 3.5.3:
- New estimator: LPDiD (Local Projections DiD; Dube, Girardi, Jorda &
  Taylor 2025), exported from the top-level package with full API docs.
- PlaceboTests: new optional `treatment` param on placebo_group_test,
  fake-group path now filters ever-treated by default, and
  permutation_test reports the (1+count)/(B+1) randomization-inference
  p-value.
- ~78-84% peak-memory reduction in the multiplier-bootstrap estimators
  (Callaway-Sant'Anna, EfficientDiD, HeterogeneousAdoptionDiD) via
  block-tiled weight generation.
- Methodology validation promoted to Complete: TwoStageDiD, PlaceboTests,
  Survey Data Support.
- Security: pyo3 + numpy 0.28 -> 0.29 (RUSTSEC-2026-0176/0177); deps and
  CI hardening (blas-src, checkout v7, release-build guard).
- Numerous perf and rank-deficiency correctness fixes across linalg,
  imputation, two-stage, conley, spillover, and continuous DiD.

Promotes the CHANGELOG [Unreleased] section to [3.6.0] - 2026-06-29 and
syncs the version across __init__.py, pyproject.toml, rust/Cargo.toml,
llms-full.txt, and CITATION.cff.

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

Merge pull request #547 from igerber/release/3.5.3

Release v3.5.3

Merge pull request #536 from igerber/release/3.5.2

Release v3.5.2: version bump + CHANGELOG reconciliation

Merge pull request #526 from igerber/release/3.5.1

Merge pull request #516 from igerber/release/3.5.0

Bump version to 3.5.0

Merge pull request #494 from igerber/release/3.4.2

Bump version to 3.4.2

Merge pull request #480 from igerber/release/3.4.1

Release 3.4.1: SpilloverDiD survey + Conley lifts, SunAbraham vcov_type, WLS-CR2 BM, methodology-tracker promotions

Merge pull request #470 from igerber/release/3.4.0

Release 3.4.0: SpilloverDiD (Butts 2021), Bacon R-parity goldens, agent-discoverability surface, PreTrendsPower R-parity audit

Merge pull request #445 from igerber/release/3.3.3

Release 3.3.3: Conley spatial-HAC SE, HAD stratified-survey Stute bootstrap, dCDH by_path × survey_design, Tutorials 21+22