infra: add a boostdeps counting bot

[Becheler]

Before submitting

• This PR targets the develop branch.
• I searched for an existing PR or issue covering the same change.
• My contribution is licensed under the Boost Software License 1.0.

Type of change

• Bug fix
• New feature or API addition
• Refactor (no behavior change)
• Documentation
• Build, CI, or tooling
• Other (specify below)

Does this PR introduce a breaking change?

• Yes (describe migration impact below)
• No

What this PR does

Builds on the success of warning count bot that publishes a comment for each PR showing the delta in compiler warnings. Instead of warnings, this bot shows

1. the dependency numbers delta against develop,
2. as well as the include weight.

Motivation

As we are aiming at reducing the number of dependencies, this gives a compass with two granularity:

1. each PR adds or removes headers, changing the weight for each dep
2. when a PR drops the weight to 0, the dependency is effectively removed.

Testing

Checklist

• Existing tests pass (b2 in the test/ directory).
• New behavior is covered by a test, or this is a docs / build / refactor change.
• Documentation was updated if user-facing behavior changed.
• No new compiler warnings on the platforms I built against.

[github-actions]

Compiler-warning counts vs develop (auto-generated).
PR run 29016446722 vs develop run 28634825303 (848786f2ef).

Job	Baseline	After	Delta
macos (clang, 14)	4	44	+40
macos (clang, 17)	4	44	+40
macos (clang, 20)	4	44	+40
ubuntu (clang-19, 14)	4	4	0
ubuntu (clang-19, 17)	4	4	0
ubuntu (clang-19, 20)	4	4	0
ubuntu (clang-19, 23)	4	4	0
ubuntu (gcc-14, 14)	10	10	0
ubuntu (gcc-14, 17)	10	10	0
ubuntu (gcc-14, 20)	10	10	0
ubuntu (gcc-14, 23)	10	10	0
windows_msvc_14_3 (msvc-14.3)	971	971	0