fix: resolve AWS Bedrock / cross-region Anthropic model IDs in model-info lookup

[HumphreySun98]

Why are these changes needed?

anthropic._model_info.get_info() and get_token_limit() resolve a model's
capabilities / context window with an anchored str.startswith prefix match
against bare first-party model keys. AWS Bedrock model IDs carry a provider
namespace (anthropic.), an optional cross-region inference prefix (us.,
eu., apac., global.), and a -vN:M version suffix, e.g.
us.anthropic.claude-3-5-sonnet-20240620-v1:0. None of these match the bare
keys, so:

• get_info() raises KeyError, which breaks AnthropicBedrockChatCompletionClient
  construction when model_info is not passed explicitly (re-raised as
  "model_info is required when model name is not recognized").
• get_token_limit() silently returns the 100000 default instead of the real
  context window.

This PR normalizes the model id (strips the [<region>.]anthropic. prefix and
the trailing -vN:M suffix) before the lookup, so Bedrock IDs resolve to their
first-party model info. First-party IDs have neither part and are unaffected.

It also completes _MODEL_TOKEN_LIMITS with the Claude 4 models and -latest
aliases that were present in _MODEL_INFO but missing here, so get_token_limit()
no longer returns the default fallback for Claude 4 and the two tables stay in
sync (guarded by a new test).

Related issue number

Closes #7833

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/ (none required for this change).
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed (ran ruff, mypy, and the relevant pytest locally).

[HumphreySun98]

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[ErenAta16]

Independently re-derived _normalize_model and ran it against every Bedrock ID shape in the description plus the un-prefixed first-party case — all resolve correctly, and test_anthropic_model_client.py's new cases pass on the branch.

One thing worth flagging: #7940 is proposing the same fix for the same underlying bug on the same file, with a regex anchored to a fixed whitelist of region prefixes (us|eu|apac|global) instead of this PR's substring-split approach. I compared the two directly — for every region AWS documents today they produce identical output, but this PR's version degrades more gracefully if AWS adds a new region prefix later (it still strips the anthropic. marker regardless of what precedes it, where the anchored whitelist would silently fail to normalize an unlisted prefix and raise KeyError). This version also ships with dedicated tests, which #7940 does not. I'd lean toward this one and closing/superseding the other, but that's a maintainer call — leaving both my analysis and a note on #7940 so whoever triages it has the comparison.

[HumphreySun98]

Thanks @ErenAta16 for the thorough independent verification and the comparison with #7940 — much appreciated!