slither-read-storage: auto-detect and accept solc Standard JSON input files

[Aravinds2511]

Fixes #2777

Problem

slither-read-storage rejected any target that wasn't a .sol file or a
project directory. Feeding it a solc Standard JSON input file (as produced by
solc --standard-json, or hand-built, per the Standard JSON input
format)
failed with:

slither.exceptions.SlitherError: Invalid compilation:
0424.json is not the expected format '.sol'

Root cause

The error comes from crytic-compile's Solc platform, which only accepts
.sol files. crytic-compile already ships a SolcStandardJson platform
(NAME = "Solc-json") that reads a Standard JSON input file directly, but
it's never auto-selected for .json targets — its is_supported() is
inherited unchanged from Solc (target.endswith(".sol")). The only way to
reach it today is the undocumented --compile-force-framework solc-json flag.

Fix

slither-read-storage's main() now checks whether the given target is a
.json file containing the two keys that define a solc Standard JSON input
("language", "sources"). If so, and the user hasn't already passed
--compile-force-framework, it's set to solc-json automatically. Detection
is safe on missing files, non-JSON files, and malformed JSON — it just
returns False and falls through to the original, clear error message.

Docs updated in docs/src/tools/ReadStorage.md to document the new
contract_source behavior and add a usage example.

Testing

Added to tests/tools/read-storage/test_read_storage.py:

• test_is_solc_standard_json — unit tests of the detection helper (valid
  Standard JSON, non-standard JSON, non-JSON file, missing file, malformed
  JSON syntax).
• test_read_storage_from_standard_json — end-to-end test that runs the real
  slither-read-storage CLI once against a .sol file and once against an
  equivalent Standard JSON file with no extra flags, and asserts the
  resulting storage layouts are identical.

$ pytest tests/tools/read-storage/test_read_storage.py -k "standard_json" -v

tests/tools/read-storage/test_read_storage.py::test_is_solc_standard_json[StorageLayout.sol-False] PASSED
tests/tools/read-storage/test_read_storage.py::test_is_solc_standard_json[not_standard.json-False] PASSED
tests/tools/read-storage/test_read_storage.py::test_is_solc_standard_json[standard_json_input.json-True] PASSED
tests/tools/read-storage/test_read_storage.py::test_read_storage_from_standard_json PASSED

4 passed, 2 deselected in 1.31s

Manual verification, reproducing the exact scenario from the issue:

$ uv run slither-read-storage 0424.json --contract-name TestVariables --json out.json

INFO:Slither-read-storage:
Contract 'TestVariables'
TestVariables.x with type uint256 is located at slot: 0

INFO:Slither-read-storage:
Name: x
Type: uint256
Slot: 0

INFO:Slither-read-storage:
Contract 'TestVariables'
TestVariables.owner with type address is located at slot: 1

INFO:Slither-read-storage:
Name: owner
Type: address
Slot: 1

INFO:Slither-read-storage:
Contract 'TestVariables'
TestVariables.paused with type bool is located at slot: 1

INFO:Slither-read-storage:
Name: paused
Type: bool
Slot: 1

$ cat out.json

{
    "x": {
        "name": "x",
        "type_string": "uint256",
        "slot": 0,
        "size": 256,
        "offset": 0,
        "value": null,
        "elems": {}
    },
    "owner": {
        "name": "owner",
        "type_string": "address",
        "slot": 1,
        "size": 160,
        "offset": 0,
        "value": null,
        "elems": {}
    },
    "paused": {
        "name": "paused",
        "type_string": "bool",
        "slot": 1,
        "size": 8,
        "offset": 160,
        "value": null,
        "elems": {}
    }
}

No extra flags required — matches the exact command from the issue report.

Scope note for maintainers

This fix is scoped to slither-read-storage only. A more general fix — giving
SolcStandardJson.is_supported() real content-based detection in
crytic-compile — would let every Slither tool accept Standard JSON targets
directly, not just read_storage. Happy to open a follow-up issue/PR there
if that's of interest.

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