Allow RPC calls using block hash or number of latest block

[cptartur]

Usage related changes

• Currently, in many places in the RPC, it is required that the users uses "latest" as block hash/number. With this PR it is also possible to use a block_hash or block_number if they belong to the latest block.
• This PR allows making calls with block tag "pending" block, though it is still treated as a "latest" block (up to discussion if this should be included).
• Changed fixtures using pytest.mark.parametrize usages with indirect=True, to parametrized fixtures.

Development related changes

None

Checklist:

• Applied formatting - ./scripts/format.sh
• No linter errors - ./scripts/lint.sh
• Performed code self-review
• Rebased to the last commit of the target branch (or merged it into my branch)
• Documented the changes
• Linked the issues which this PR resolves
• Updated the tests
• All tests are passing

[FabijanC]

Thanks for the contribution!

1. Accepted block IDs can be documented in page/docs/guide/json-rpc-api.md.
2. Currently only "latest" is tested. Shouldn't providing "pending" also be tested?

[cptartur]

1. Will be added
2. I wasn't sure if we want to include "pending", for me it seems like a logical addition since "pending" is supported in gateway as far as I know. I'll extend the test to cover pending block.

[cptartur]

Addressed the comments. I've also unchecked "tests are passing" because test/test_postman.py::test_postman suddenly stopped working. I suspect it's a problem with some local configuration on my end so if tests could be run on your end we could verify that.

[FabijanC]

Cloned your fork, postman test is passing.