Remove unused variables, fields, and captures

[eddyashton]

While we're improving clang-tidy coverage (#7449, #7451) and adding a lot of [[nodiscard]] attributes I realised these aren't having the desired impact. Because we're also compiling with -Wno-unused, and ignoring all sorts of unused things.

I've fiddled with a few options, and I think what we actually want is -Wno-unused-parameter (because you have to implement a signature, but sometimes an argument isn't for you! Removing the name or adding an attribute are both ugly band-aids), and -Wno-unused-function (because we have lots of header-defined static functions used in some compilation units but not others. Would be great to find which are truly globally unused, but that's harder).

In practice this mostly finds unused lambda captures ([this] -> []), a few unused variables and fields (I think missed during refactors or block copy-pastes), and a few unchecked results of JSWrappedValue::set... calls. I've added check-and-throw blocks so the latter compile, but I think this is ugly; if no-one wants the return values, then we should probably stop returning them entirely, and simply swallow-or-throw within the set... call itself. I've now added [[nodiscard]] to ALL the set functions, and wrapped all call-points in a new JS_CHECK_OR_THROW macro

[Copilot]

Pull Request Overview

This PR improves compiler warning coverage by replacing the broad -Wno-unused flag with more targeted -Wno-unused-parameter and -Wno-unused-function flags. This enables detection of genuinely unused variables, fields, and lambda captures while still allowing unused function parameters (required by interface signatures) and unused static header functions.

• Removes unused lambda captures (primarily [this] where the lambda body doesn't use member variables/functions)
• Removes unused local variables and fields identified by the stricter warning settings
• Adds error checking for some previously unchecked JSWrappedValue::set... return values

Reviewed Changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
cmake/preproject.cmake	Replaces -Wno-unused with more specific -Wno-unused-parameter and -Wno-unused-function to enable better unused code detection
src/tasks/ordered_tasks.cpp	Removes unused [this] lambda capture where only the action parameter is used
src/quic/quic_session.h	Removes unused written variable that accumulated bytes written but wasn't used
src/node/rpc/node_frontend.h	Removes unused [this] captures from multiple lambdas and unused local variables config and service_config
src/node/rpc/jwt_management.h	Removes unused issuer_constraints from lambda capture list (still used elsewhere in the function)
src/node/quote.cpp	Removes unused digest variable
src/node/node_state.h	Removes unused service_config local variable
src/node/gov/handlers/proposals.h	Adds error checking for set_bool() return value
src/kv/store.h	Removes unused fields size_since_chunk and chunk_threshold
src/kv/serialised_entry_format.h	Adds [[maybe_unused]] to max_entry_size constant (used only in assertions)
src/js/registry.cpp	Removes unused [this] capture and unused rt variable
src/js/extensions/ccf/request.cpp	Adds error checking for multiple set() and set_null() return values when populating JS objects
src/js/extensions/ccf/historical.cpp	Removes unused view and seqno variables
src/js/extensions/ccf/crypto.cpp	Removes unused exception variable (though this introduces a bug)
src/endpoints/authentication/cose_auth.cpp	Removes unused gov_msg_proposal_created_at variable
src/crypto/csr.h	Removes unused icrt variable
samples/apps/programmability/programmability.cpp	Removes unused [this] lambda capture
samples/apps/logging/logging.cpp	Removes many unused [this] lambda captures and unused make_handle lambda function
samples/apps/basic/basic.cpp	Removes unused [this] lambda capture

[eddyashton]

@copilot review this PR again now it has been updated.