standardlastprofile 2.0.0

This release (finally) adds gas standard load profiles (SLPs) alongside the
existing electricity profiles. We introduce an updated interface for
electricity SLPs too. All renames and deprecations below are backward compatible.

New functions

• slp_electricity() is the new primary function for generating electricity
  SLPs. It replaces slp_generate() with a cleaner
  interface: no state_code argument and no restriction on the date range
  (previously limited to 1990–2073 by the built-in holiday data).

• slp_gas() implements the BDEW/VKU/GEODE synthetic procedure for gas
  SLPs (SigLinDe method). It supports all 15 gas profile IDs
  defined in the BDEW Leitfaden, as of 2025-10-28 (HEF, HMF, HKO,
  GKO, GHA, GMK, GBD, GBH, GWA, GGA, GBA, GGB, GPD,
  GMF, GHD). The function takes daily temperatures and a kundenwert
  (kWh/day), and returns daily gas consumption in kWh. A variant argument
  selects between SigLinDe variant (German: "Ausprägung") "34"
  (57 % linear component) and "33" (45 % linear component).

• slp_gas_kundenwert() derives the kundenwert from a full reference year
  of daily temperatures and an annual consumption target. You might use this in
  a two-step workflow: compute KW once from a representative year, then pass
  the result as kundenwert to slp_gas() for any shorter period. Daily mean
  temperatures can be obtained e.g. from the DWD open-data archive, e.g. via the
  rdwd package; see the gas SLP article on the package website
  for a complete fetch-to-profile walkthrough.

• slp_gas_siglinde() exposes the low-level dimensionless daily heating
  demand function h(θ) used internally by slp_gas(). It is exported so
  that users with custom or region-specific coefficients (e.g. state-level
  parameters such as BW_HEF03 for Baden-Württemberg) can compute h(θ)
  directly and build their own profiles.

• slp_gas_coefficients() returns the SigLinDe profile function coefficients
  (A, B, C, D, θ₀, mH, bH, mW, bW) for one or more gas profiles as a data
  frame. Supports both variants ("34", "33").

• slp_gas_weekday_factors() returns the weekday scaling factors (F_WT) for
  one or more gas profiles as a data frame with columns profile_id,
  day, and f_wt.

• Nationwide German public holidays are now computed via the
  Anonymous Gregorian Easter algorithm rather than looked up in a precomputed
  table. Coverage is open-ended from 1990 onward (the year German Unity Day
  was introduced); the previous 2073 / 2099 caps no longer apply. State-level
  holidays are no longer included; use the holidays argument to supply
  custom dates.

• slp_info() now accepts gas profile IDs too (HEF, HMF, HKO, etc.)
  in addition to electricity IDs, and respects the language argument for
  both. Electricity and gas IDs can be mixed freely in a single call.

Deprecations

• The dataset slp has been renamed to slp_electricity_profiles. The package
  no longer ships under the old name, but accessing slp still returns the data
  and emits a lifecycle deprecation warning pointing to the new name. The
  shim will be removed in a future release.

Superseded

• slp_generate() is now superseded in favour of slp_electricity(). It
  remains in the package and will not be removed for now, but new code should
  use slp_electricity() instead.

Breaking changes

• Passing state_code to slp_generate() now throws an error (previously a
  warning since version 1.1.0). Use the holidays argument of
  slp_electricity() to supply custom holiday dates.