Create signedVarInt reader

[pablitovicente]

Description

Create function signedVarint(buffer, schema) => value

Motivation

lisk-codec will include a set of Readers for each data type defined in the LIP, to that end
we need a function to read Signed VarInts.

Acceptance Criteria

• signedVarint() should accept a buffer representation of a signed varint value
• signedVarint() returns either a signed number or a BigInt (this is controlled by the schema)
• Code should be optimised for speed as much as possible
• Full test coverage
• Performance stats are provided based on the reading of values of different sizes and measure the reading of 100, 500, 1000, 30000 signedVarint

Additional Information

Check if it will make sense to implement varints in same issue.

Related issues: #5200