Add `spre` and `spost` methods for `ComposedOperator` and cache propagator in every time evolution solver #999

	# Enforces the update of the file CHANGELOG.md on every pull request
	# Can be skipped with the `Skip ChangeLog` label
	name: ChangeLog Update Check
	on:
	pull_request:
	types: [opened, synchronize, reopened, ready_for_review, labeled, unlabeled]

	jobs:
	changelog:
	runs-on: ubuntu-latest
	if: ${{ !github.event.pull_request.draft }}
	steps:
	# check whether CHANGELOG.md is updated
	- uses: dangoslen/changelog-enforcer@v3
	with:
	skipLabels: 'Skip ChangeLog'

	# check whether the format of CHANGELOG.md is correct
	- uses: actions/checkout@v5
	- uses: julia-actions/setup-julia@v2
	with:
	version: '1'
	- name: Install and Run Changelog
	run: \|
	julia -e 'import Pkg; Pkg.add("Changelog")'
	julia -e 'using Changelog; Changelog.generate(Changelog.CommonMark(), "CHANGELOG.md"; repo = "qutip/QuantumToolbox.jl")'

	- name: CHANGELOG Format Check
	run: \|
	julia -e '
	output = Cmd(`git diff --name-only`) \|> read \|> String
	if output == ""
	exit(0)
	else
	@error "The format of CHANGELOG.md is not correct !!!"
	write(stdout, "Please format it by running the following command:\n")
	write(stdout, "make changelog")
	exit(1)
	end'

Provide feedback