chore: Eslint v9 (#24)

## Changes

Converted the configuration file to flat config and unified to config
file style. Otherwise same rules are earlier, but some new rules
disabled (see "Future improvements").

The `bin` directory is also now included as a source directory and
therefore `eslint` checks also those files.

Also small changes to code to fix some `eslint` warnings. These
modifications don't change any functionality.

## Future improvements

- Avoid using `any` type, i.e. enable these rules:
  - `@typescript-eslint/no-unsafe-argument`
  - `@typescript-eslint/no-unsafe-assignment`
  - `@typescript-eslint/no-unsafe-call`
  - `@typescript-eslint/no-unsafe-member-access`
  - `@typescript-eslint/no-unsafe-return`
- Implement safer promise handling, i.e. enable these rules:
  - `@typescript-eslint/no-floating-promises`
  - `@typescript-eslint/no-misused-promises`
  - `@typescript-eslint/require-await`

Author: teogeb

.eslintignore

@@ -0,0 +1,89 @@
+import streamr from 'eslint-config-streamr-ts'
+
+export default [
+    {
+        ignores: [
+            'node_modules/**',
+            'dist/**'
+        ]
+    },
+    ...streamr,
+    {
+        rules: {
+            'class-methods-use-this': 'error',
+            'eol-last': 'error',
+            'no-console': ['error', {
+                allow: ['warn', 'error', 'info']
+            }],
+            'no-restricted-imports': ['error', {
+                patterns: ["*/dist"]
+            }],
+            'no-unused-vars': 'off',
+            'prefer-arrow-callback': 'error',
+            '@typescript-eslint/consistent-indexed-object-style': 'error',
+            '@typescript-eslint/consistent-type-assertions': 'error',
+            '@typescript-eslint/consistent-type-definitions': 'error',
+            '@typescript-eslint/default-param-last': 'error',
+            '@typescript-eslint/no-confusing-non-null-assertion': 'error',
+            '@typescript-eslint/no-duplicate-enum-values': 'error',
+            '@typescript-eslint/no-empty-function': 'error',
+            '@typescript-eslint/no-extraneous-class': 'error',
+            '@typescript-eslint/no-inferrable-types': 'off',
+            '@typescript-eslint/no-invalid-this': 'error',
+            '@typescript-eslint/no-invalid-void-type': 'error',
+            '@typescript-eslint/no-non-null-asserted-nullish-coalescing': 'error',
+            '@typescript-eslint/no-require-imports': 'error',
+            '@typescript-eslint/no-unused-expressions': 'error',
+            '@typescript-eslint/no-unused-vars': ['error', {
+                vars: 'all',
+                args: 'all',
+                argsIgnorePattern: '^_',
+                varsIgnorePattern: '^_',
+                caughtErrorsIgnorePattern: '^_'
+            }],
+            '@typescript-eslint/no-useless-constructor': 'error',
+            '@typescript-eslint/no-useless-empty-export': 'error',
+            '@typescript-eslint/prefer-for-of': 'error',
+            '@typescript-eslint/prefer-function-type': 'error',
+            '@typescript-eslint/prefer-literal-enum-member': 'error',
+            '@stylistic/brace-style': ['error', '1tbs', {
+                allowSingleLine: true
+            }],
+            '@stylistic/comma-spacing': 'error',
+            '@stylistic/func-call-spacing': 'error',
+            '@stylistic/keyword-spacing': 'error',
+            '@stylistic/member-delimiter-style': ['error', {
+                singleline: { delimiter: 'comma' },
+                multiline: { delimiter: 'none' }
+            }],
+            '@stylistic/object-curly-spacing': ['error', 'always'],
+            '@typescript-eslint/restrict-template-expressions': ['error', { 
+                allowAny: false,
+                allowBoolean: true,
+                allowNullish: true,
+                allowNumber: true,
+                allowRegExp: true,
+                allowNever: true,
+                allow: [{ from: 'lib', name: ['Error'] }]
+            }],
+            '@stylistic/space-before-blocks': 'error',
+            '@stylistic/space-before-function-paren': ['error', {
+                anonymous: 'never',
+                named: 'never',
+                asyncArrow: 'always'
+            }],
+            '@stylistic/space-infix-ops': 'error',
+            'promise/no-promise-in-callback': 'error',
+
+            // TODO maybe we could enable some of these
+            '@typescript-eslint/no-floating-promises': 'off',
+            '@typescript-eslint/no-misused-promises': 'off',
+            '@typescript-eslint/no-unsafe-argument': 'off',
+            '@typescript-eslint/no-unsafe-assignment': 'off',
+            '@typescript-eslint/no-unsafe-call': 'off',
+            '@typescript-eslint/no-unsafe-member-access': 'off',
+            '@typescript-eslint/no-unsafe-return': 'off',
+            '@typescript-eslint/require-await': 'off'
+        }
+    }
+]