Return type

[shaleenji]

PR Title

Add shared OperationResult type for explicit error propagation

PR Body

Summary

This PR introduces a shared ndd::OperationResult<T> type in src/utils/types.hpp.

OperationResult is intended to become the standard lightweight return type for operations that need to report success or failure without throwing exceptions. It supports both status-only functions and functions that return a value.

ndd::OperationResult<> status;
ndd::OperationResult<ndd::RoaringBitmap> bitmap_result;

Why

Several parts of the codebase currently handle errors inconsistently: some functions throw, some log and continue, and some return fallback values like false or an empty bitmap even when the real issue is a storage failure.

That makes it hard for callers to distinguish between valid empty results and actual failures.

OperationResult gives us a common pattern for propagating errors upward so callers can decide whether to log, retry, return an API error, or abort the current operation.

Design

OperationResult<T> contains:

• code: 0 means success; non-zero codes are operation-specific.
• message: optional human-readable failure context.
• value: optional result payload for functions that return data.
• ok(): convenience helper for success checks.

The default type is std::monostate, so status-only operations can use:

ndd::OperationResult<> result;

Future Usage

Follow-up changes will use this type across the filter subsystem first, especially for paths that currently swallow failures or return ambiguous defaults.

Examples:

ndd::OperationResult<> add_filters_from_json_batch(...);

ndd::OperationResult<ndd::RoaringBitmap>
computeFilterBitmap(...);

Each function using OperationResult should document its local result codes above the function definition. Callers will use those codes to map failures to logs and API responses.

For example:

// Result codes:
// 0 = success
// 1 = invalid filter JSON
// 2 = unsupported field type
// 100 = MDBX write failure
ndd::OperationResult<> add_filters_from_json_batch(...);

Notes

This PR only adds the shared type. It does not yet change filter behavior or API error handling. Subsequent PRs will wire this into filter writes, reads, MDBX error paths, logging, and API response mapping.

[github-actions]

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