Document method enum indexing invariant

[Copilot]

Overview

This PR adds documentation to the http_proto::method enumeration to explicitly state an important invariant: that the enumeration constants begin at 0 and increment by 1, making them suitable for use as indexes into compact arrays.

Changes

Updated the documentation comment for enum class method in include/boost/http_proto/method.hpp to include a new @par Enumeration Constants section that guarantees:

• The first constant (method::unknown) starts at 0
• Each subsequent constant is incremented by exactly one
• This property makes the constants suitable for use as indexes into a compact array

Example Use Case

With this documented guarantee, users can now confidently write code like:

const char* method_names[34] = { /* ... */ };
method m = method::get;
const char* name = method_names[static_cast<int>(m)];  // Safe to use as array index

Verification

The enumeration values were verified to follow this invariant:

• method::unknown = 0
• method::delete_ = 1
• method::get = 2
• ...
• method::unlink = 33

All 34 constants are sequential with no gaps.

Impact

This is a documentation-only change with no modifications to code or enum values. The invariant has always been true for this enum; this PR simply documents the guarantee for library users.

Fixes #[issue_number]

Original prompt

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This section details on the original issue you should resolve

<issue_title>http_proto::method enumeration additional invariants</issue_title>
<issue_description>The documentation comment for the http_proto::method enumeration should state an additional guarantee: That the first constant starts at 0 (zero), and each subsequent constant is incremented by one, making the constants suitable for use as indexes into a compact array. Any fixes for this issue should limit changes to ONLY the documentation comment for http_proto::method.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #179

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[vinniefalco]

rename this section to simply "Values"

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.48%. Comparing base (1a8a81c) to head (4d2c852).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #180   +/-   ##
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  Coverage    92.48%   92.48%           
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  Files           71       71           
  Lines         4854     4854           
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  Hits          4489     4489           
  Misses         365      365           

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