Implement half of weaver registry stats for V2.

[jsuereth]

Optimistically did this using some AI assistance. Still think there's room to clean up some of these statistics, but it still offers some good insights on V2.

Note: I did NOT implement any refinement based stats yet.

Example output:

$ ./target/debug/weaver registry stats --v2
Compute statistics on the registry `https://github.com/open-telemetry/semantic-conventions.git[model]`
ℹ No registry manifest found: /home/joshuasuereth/.weaver/vdir_cache/repo.AOZQW9pJUNkb/model/registry_manifest.yaml
✔ `main` semconv registry `https://github.com/open-telemetry/semantic-conventions.git[model]` loaded (229 files)
✔ `main` semconv registry resolved
Resolved Telemetry Schema Stats:
Registry
- Attributes
  - count: 1043
  - deprecated: 130
  - type breakdown: 
    - string: 618
    - int: 112
    - enum(card:002): 51
    - string[]: 34
    - enum(card:001): 26
    - enum(card:003): 26
    - template[string]: 26
    - boolean: 24
    - enum(card:005): 23
    - enum(card:004): 19
    - double: 14
    - enum(card:006): 9
    - enum(card:009): 9
    - any: 8
    - enum(card:008): 7
    - enum(card:007): 6
    - enum(card:012): 6
    - template[string[]]: 6
    - enum(card:011): 5
    - enum(card:016): 3
    - enum(card:015): 2
    - enum(card:017): 2
    - enum(card:041): 2
    - enum(card:014): 1
    - enum(card:019): 1
    - enum(card:021): 1
    - enum(card:033): 1
    - enum(card:054): 1
  - stability breakdown: 
    - development: 861
    - stable: 174
    - release_candidate: 8
- Attribute Groups
  TODO
- Entities
  - count: 55
  - deprecated: 1
  - stability breakdown: 
    - development: 53
    - stable: 2
  - total with note: 1
   - entity identity length distribution: 
      - 0: 36
      - 1: 14
      - 2: 4
      - 3: 1
- Events
  - count: 19
  - deprecated: 6
  - stability breakdown: 
    - release_candidate: 1
    - development: 17
    - stable: 1
  - total with note: 9
- Metrics
  - count: 486
  - deprecated: 68
  - stability breakdown: 
    - stable: 51
    - development: 435
  - total with note: 299
  - instrument breakdown: 
    - updowncounter: 243
    - counter: 120
    - gauge: 65
    - histogram: 58
  - unit breakdown: 
    - By: 120
    - s: 65
    - {pod}: 44
    - 1: 24
    - {cpu}: 21
    - {connection}: 18
    - {span}: 13
    - {request}: 11
    - {node}: 9
    - {error}: 7
    - {packet}: 7
    - {count}: 6
    - {log_record}: 6
    - {message}: 6
    - {object}: 6
    - {operation}: 6
    - ms: 5
    - {fault}: 5
    - {thread}: 5
    - Cel: 4
    - W: 4
    - {attempt}: 4
    - {hugepage}: 4
    - {persistentvolumeclaim}: 4
    - Hz: 3
    - V: 3
    - {class}: 3
    - {container}: 3
    - {inode}: 3
    - {timeout}: 3
    - J: 2
    - rpm: 2
    - {client}: 2
    - {collection}: 2
    - {data_point}: 2
    - {exception}: 2
    - {file_descriptor}: 2
    - {instance}: 2
    - {job}: 2
    - {procedure}: 2
    - {process}: 2
    - {record}: 2
    - {request_unit}: 2
    - {sign_in}: 2
    - {sign_out}: 2
    - {work_item}: 2
    - %: 1
    - By/s: 1
    - {Hz}: 1
    - {allocation}: 1
    - {assembly}: 1
    - {authrefresh}: 1
    - {buffer}: 1
    - {challenge}: 1
    - {change}: 1
    - {coldstart}: 1
    - {contention}: 1
    - {context_switch}: 1
    - {contributor}: 1
    - {fh}: 1
    - {forbid}: 1
    - {goroutine}: 1
    - {handshake}: 1
    - {invocation}: 1
    - {line}: 1
    - {match_attempt}: 1
    - {method}: 1
    - {namespace}: 1
    - {ref}: 1
    - {repository}: 1
    - {restart}: 1
    - {retransmit}: 1
    - {revision}: 1
    - {row}: 1
    - {run_queue_item}: 1
    - {run}: 1
    - {timer}: 1
    - {token}: 1
- Spans
  - count: 42
  - deprecated: 0
  - stability breakdown: 
    - development: 38
    - stable: 4
  - total with note: 37
  - span kind breakdown: 
    - Internal: 8
    - Server: 11
    - Client: 23
Refinements
  TODO

Total execution time: 2.303995894s

[codecov]

Codecov Report

❌ Patch coverage is 77.52809% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.3%. Comparing base (1511626) to head (8368f18).
⚠️ Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/weaver_resolved_schema/src/v2/registry.rs	81.1%	16 Missing ⚠️
crates/weaver_resolved_schema/src/v2/mod.rs	0.0%	3 Missing ⚠️
...rates/weaver_resolved_schema/src/v2/refinements.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1037     +/-   ##
=======================================
+ Coverage   78.7%   79.3%   +0.6%     
=======================================
  Files         82      83      +1     
  Lines       6612    7122    +510     
=======================================
+ Hits        5204    5654    +450     
- Misses      1408    1468     +60     

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