feat: add internal spec for debug-info

[djolertrk]

This introduces the compiler-side model for carrying Solidity semantic debug info through the Yul pipeline, including AST-ID based reattachment across Yul reparse.
Current scope is intentionally narrow and we will add more entries into it once we are okay with the proposal on a high-level.

See docs/internals/ethdebug_internal_metadata.rst for more detailed explanation of the design.

[djolertrk]

cc @nikola-matic @clonker

[nikola-matic]

Can you fix the build (the comment I left below should do it), and then can you drop a solc-bench in here.

[nikola-matic]

Suggested change

	std::vector<SemanticDebugVariable> variableDefinitions;
	std::vector<SemanticDebugVariable> variableDefinitions = {};

Since you're using named initializers, this should fix the build.

[djolertrk]

@nikola-matic I fixed the build and here is the solc-bench output:

Benchmark          Metric         ir-ethdebug           ir                   Δ%        winner
-----------------  -------------  --------------------  -------------------  --------  ------
prb-math-4.1.1     cpu_time       12.1321s ± 0.4704s    10.0406s ± 0.3165s   +20.83%   ir
                   creation_size  592,270 ± 0           592,270 ± 0          0.0%      tie
                   peak_rss       2044080 ± 96536 MiB   1295600 ± 52003 MiB  +57.77%   ir
                   runtime_size   589,640 ± 0           589,640 ± 0          0.0%      tie
                   wall_time      12.8027s ± 0.6464s    10.4773s ± 0.4362s   +22.2%    ir
                   ethdebug_size  44.80 MiB ± 0.00 MiB  n/a                  N/A       n/a

forge-std-1.16.1   cpu_time       11.8554s ± 0.2979s    10.2449s ± 0.1482s   +15.72%   ir
                   creation_size  725,280 ± 0           725,280 ± 0          0.0%      tie
                   peak_rss       1554816 ± 70351 MiB   796144 ± 9474 MiB    +95.29%   ir
                   runtime_size   698,851 ± 0           698,851 ± 0          0.0%      tie
                   wall_time      12.1417s ± 0.3452s    10.4575s ± 0.1829s   +16.1%    ir
                   ethdebug_size  44.94 MiB ± 0.00 MiB  n/a                  N/A       n/a

morpho-blue-1.0.0  cpu_time       16.3965s ± 0.7634s    14.7222s ± 1.0004s   +11.37%   ~noise
                   creation_size  1,261,421 ± 0         1,261,421 ± 0        0.0%      tie
                   peak_rss       1824912 ± 50816 MiB   921792 ± 34683 MiB   +97.97%   ir
                   runtime_size   1,251,246 ± 0         1,251,246 ± 0        0.0%      tie
                   wall_time      16.9356s ± 0.9110s    15.0786s ± 1.1852s   +12.32%   ~noise
                   ethdebug_size  57.38 MiB ± 0.00 MiB  n/a                  N/A       n/a

solmate-6          cpu_time       6.9523s ± 0.1573s     6.0532s ± 0.3605s    +14.85%   ir
                   creation_size  540,758 ± 0           540,758 ± 0          0.0%      tie
                   peak_rss       919888 ± 33125 MiB    379440 ± 18556 MiB   +142.43%  ir
                   runtime_size   523,577 ± 0           523,577 ± 0          0.0%      tie
                   wall_time      7.1106s ± 0.1848s     6.2070s ± 0.4427s    +14.56%   ir
                   ethdebug_size  30.92 MiB ± 0.00 MiB  n/a                  N/A       n/a

Thank you!