Typings are incompatible with jest

Because `truffle-typings` includes `chai` and `mocha` constants, the same project can't use `jest` for tests.

Build errors:
```
node_modules/@types/jest/index.d.ts:33:13 - error TS2403: Subsequent variable declarations must have the same type. Variable 'beforeEach' must be of type 'HookFunction', but here has type 'Lifecycle'.

33 declare var beforeEach: jest.Lifecycle;
~~~~~~~~~~

node_modules/@types/mocha/index.d.ts:2680:13
2680 declare var beforeEach: Mocha.HookFunction;
~~~~~~~~~~
'beforeEach' was also declared here.

node_modules/@types/jest/index.d.ts:35:13 - error TS2403: Subsequent variable declarations must have the same type. Variable 'afterEach' must be of type 'HookFunction', but here has type 'Lifecycle'.

35 declare var afterEach: jest.Lifecycle;
~~~~~~~~~

node_modules/@types/mocha/index.d.ts:2698:13
2698 declare var afterEach: Mocha.HookFunction;
~~~~~~~~~
'afterEach' was also declared here.

node_modules/@types/jest/index.d.ts:36:13 - error TS2403: Subsequent variable declarations must have the same type. Variable 'describe' must be of type 'SuiteFunction', but here has type 'Describe'.

36 declare var describe: jest.Describe;
~~~~~~~~

node_modules/@types/mocha/index.d.ts:2714:13
2714 declare var describe: Mocha.SuiteFunction;
~~~~~~~~
'describe' was also declared here.

node_modules/@types/jest/index.d.ts:38:13 - error TS2403: Subsequent variable declarations must have the same type. Variable 'xdescribe' must be of type 'PendingSuiteFunction', but here has type 'Describe'.

38 declare var xdescribe: jest.Describe;
~~~~~~~~~

node_modules/@types/mocha/index.d.ts:2735:13
2735 declare var xdescribe: Mocha.PendingSuiteFunction;
~~~~~~~~~
'xdescribe' was also declared here.

node_modules/@types/jest/index.d.ts:39:13 - error TS2403: Subsequent variable declarations must have the same type. Variable 'it' must be of type 'TestFunction', but here has type 'It'.

39 declare var it: jest.It;
~~

node_modules/@types/mocha/index.d.ts:2749:13
2749 declare var it: Mocha.TestFunction;
~~
'it' was also declared here.

node_modules/@types/jest/index.d.ts:41:13 - error TS2403: Subsequent variable declarations must have the same type. Variable 'xit' must be of type 'PendingTestFunction', but here has type 'It'.

41 declare var xit: jest.It;
~~~

node_modules/@types/mocha/index.d.ts:2770:13
2770 declare var xit: Mocha.PendingTestFunction;
~~~
'xit' was also declared here.

node_modules/@types/jest/index.d.ts:42:13 - error TS2403: Subsequent variable declarations must have the same type. Variable 'test' must be of type 'TestFunction', but here has type 'It'.

42 declare var test: jest.It;
~~~~

node_modules/@types/mocha/index.d.ts:2763:13
2763 declare var test: Mocha.TestFunction;
~~~~
'test' was also declared here.

node_modules/@types/jest/index.d.ts:45:15 - error TS2451: Cannot redeclare block-scoped variable 'expect'.

45 declare const expect: jest.Expect;
~~~~~~

node_modules/truffle-typings/index.d.ts:11:15
11 declare const expect: Chai.ExpectStatic;
~~~~~~
'expect' was also declared here.

node_modules/truffle-typings/index.d.ts:11:15 - error TS2451: Cannot redeclare block-scoped variable 'expect'.

11 declare const expect: Chai.ExpectStatic;
~~~~~~

node_modules/@types/jest/index.d.ts:45:15
45 declare const expect: jest.Expect;
~~~~~~
'expect' was also declared here.
```

Start by reproducing the TypeScript build errors involving node_modules/truffle-typings/index.d.ts, @types/jest/index.d.ts, and @types/mocha/index.d.ts. Trace how the typings expose global test declarations, then verify that a project using Jest no longer gets the reported declaration conflicts while Truffle typings remain usable.

Written by the indexing model from the issue text.