Add SubFile.readable

[pressler-vsc]

Description

When I tried to use hashlib.file_digest with a SubFile, I got an error because it was looking for a readable method that SubFile did not yet implement

While adding this method, I was curious why the static typing didn't find this. One reason is that many of the SubFile methods weren't type-annotated, but a bigger problem is that the protocol we declare does not match what we're doing in SubFile. Until Python gets its act together w.r.t. file-like objects, I propose just using typing.Any

Demo

import hashlib

import jbpy

nitf_path = "/host_shared/JITC_QuickLook_NITF/Quick-Look-Set-v2023.11.30/1. Format Constructs/POS/NITF_FMT_POS_01.NITF"

with open(nitf_path, "rb") as f:
    j = jbpy.Jbp()
    j.load(f)
    print(
        hashlib.file_digest(
            j["ImageSegments"][0]["Data"].as_filelike(f), "sha1"
        ).hexdigest()
    )

In main

$ python tmp.py 
Traceback (most recent call last):
ValueError: '<jbpy.core.SubFile object at 0x7fa756cefa10>' is not a file-like object in binary reading mode.

In this branch

$ python tmp.py 
90cea18ce80b94732a5cc532331db5123411c471