feat(common): support null parameters in eth_call udf

[shiyasmohd]

• Allow optional parameters (from, input_data) to accept NULL values in eth_call udf
• Added integration tests
• Update feature docs

Example

// Before
SELECT eth_rpc.eth_call(
    arrow_cast(NULL,'FixedSizeBinary(20)'),
    evm_encode_hex('0x0000000000000000000000000000000000000000'),
    arrow_cast(NULL,'Binary'),
    'latest'
)

// After
SELECT eth_rpc.eth_call(
    NULL,
    evm_encode_hex('0x0000000000000000000000000000000000000000'),
    NULL,
    'latest'
)