Ledger DB lock improvements (#74)

# Description

Rework the locking logic for the ledger DB RAW lock. There are mainly 4 places where locking happens:
- background thread that flushes regularly: uses a **write** lock while writing the differences only.
- background thread that creates snapshots: holds a **read** lock for the duration of the snapshot
- forging loop: **quick read** locking to acquire a ledger db and a value handle to get a snapshot
- queries: **quick read** locking to acquire a ledger db and a value handle

This should reduce locking issues.

There are also some side effects in the PR:
- the forging loop is again a `WithEarlyExit` block
- getting a snapshot can no longer fail s you provide the chlog and the value handle
- new policy function `onDiskShouldFlush`

Closes #43

.gitattributes

@@ -1,11 +1,4 @@
 # GitHub Linguist annotations.
-# Hide nix/.stack.nix/*.nix
-# That is stuff that is generated by nix-tools stack-to-nix
+# https://github.com/github-linguist/linguist/blob/master/docs/overrides.md
 
-nix/.stack.nix/*.nix linguist-generated=true
-.stack-to-nix.cache linguist-generated=true
-nix/.stack-pkgs.nix linguist-generated=true
-
-ouroboros-consensus-byron-test/test/golden/**/* linguist-generated=true
-ouroboros-consensus-shelley-test/test/golden/**/* linguist-generated=true
-ouroboros-consensus-cardano-test/test/golden/**/* linguist-generated=true
+ouroboros-consensus-cardano/golden/**/* linguist-generated=true

.github/workflows/checks.yml

@@ -6,15 +6,15 @@ concurrency:
 
 on:
   pull_request:
+    branches:
+      - main
   merge_group:
 
 jobs:
   consensus-changelog:
 
     name: Changelog sanity check
 
-    if: ${{ github.event_name == 'push' || !github.event.pull_request.draft }}
-
     runs-on: ubuntu-latest
 
     defaults:
@@ -29,7 +29,69 @@ jobs:
 
     - uses: actions/checkout@v3
       with:
-        ref: ${{ env.GITHUB_BASE_REF }}
+        ref: ${{ github.event.pull_request.base.ref || github.event.merge_group.base_ref }}
         path: 'main'
 
     - run: CI=1 ./this-pr/scripts/ci/check-changelogs.sh main this-pr
+
+  check-cabal-files:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Install Haskell
+      uses: input-output-hk/setup-haskell@v1
+      id: setup-haskell
+      with:
+        cabal-version: "3.10.1.0"
+
+    - uses: actions/checkout@v3
+
+    - name: Cabal check
+      run: ./scripts/ci/check-cabal-files.sh
+
+  # Enabling the assertions results in an error in IO-Sim.
+  # https://github.com/input-output-hk/io-sim/issues/94
+  # Until it is fixed, re-enabling this will only lead to blocked CI.
+
+  # cabal-project-asserts:
+
+  #   name: Cabal project asserts
+
+  #   runs-on: ubuntu-latest
+
+  #   defaults:
+  #     run:
+  #       shell: bash
+
+  #   env:
+
+  #     # current ref from: 27.02.2022
+  #     SECP256K1_REF: ac83be33d0956faf6b7f61a60ab524ef7d6a473a
+
+  #     SECP_CACHE_VERSION: "2023-04-27"
+
+  #   steps:
+
+  #   - uses: actions/checkout@v3
+
+  #   - name: Install Haskell
+  #     uses: input-output-hk/setup-haskell@v1
+  #     id: setup-haskell
+  #     with:
+  #       cabal-version: "3.10.1.0"
+  #       ghc-version: "9.2.7"
+
+  #   - name: Install build environment
+  #     run: |
+  #       sudo apt-get update
+  #       sudo apt-get -y install libsodium-dev
+
+  #   - name: Install secp256k1
+  #     uses: input-output-hk/setup-secp256k1@v1
+  #     with:
+  #       git-ref: ${{ env.SECP256K1_REF }}
+  #       cache-version: ${{ env.SECP_CACHE_VERSION }}
+
+  #   - run: |
+  #       ./scripts/ci/regen-project-asserts.sh
+  #       git --no-pager diff --exit-code